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Detecting Cyber Intrusions in Substation Networks

15 Sep

This article will describe the security requirements of IEC 61850 substations and the different approaches for detecting threats in these networks. Subsequently, an approach specifically developed for the IEC 61850 station and process bus will be described.

Let us define a cyber attack on a substation as an event where an adversary modifies, degrades, or disables a service of at least one protection, automation, or control device within the substation. Looking at Figure 1, a typical substation can be attacked through all paths marked with a number. An attacker could enter through the control center connection (1), as happened in one of the cyber-attacks in Ukraine, where the firmware of gateway devices was modified (causing their destruction). Another entry point is through engineering PCs (2) connected to substation equipment. When a protection engineer connects their PC to a relay to modify (protection) settings, malware on the PC could, in turn, install malware on the relay in a comparable way to what happened with PLCs in the Stuxnet cyber attack. Laptops used for testing the IEC 61850 system are often directly connected to the station bus which is also a potential way to infect IEDs (3). For this reason, new IEC 61850 testing tools are available which provide a cyber-secure separation between the Test PC and the substation network. This leaves the testing device itself (4) as a potential entry path. Because of this, it is important that test set vendors invest in hardening their devices to make sure that this entry path is not feasible for an attacker to exploit.



Fig. 1: Attack vectors of a substation.

Security and IEC 61850
A frequent question about cybersecurity in IEC 61850 substations is: “What happens if an attacker injects a trip GOOSE into the station bus – how can I prevent that?” For this, we should not focus on the attacker having physical access to the substation network. This situation is also possible through other measures: an infected engineering or testing PC connected to the station bus, or even that an infected IED could start injecting GOOSE. In this context, the status and sequence numbers in the GOOSE message are quite often presented as GOOSE “security mechanisms”. However, in 2019, such measures should merely be called “safety mechanisms”, because any adversary can listen to the current status and sequence number and inject suitable values. Also, the source MAC address of the GOOSE packet can be spoofed easily by the attacker. The IED receiving the GOOSE has no other option than to react on the first GOOSE received with correct source MAC and correct status/sequence number. The same of course applies to the sample counter in sampled values. The only real measure to prevent such injection attacks is by ensuring the authenticity and integrity of the message using authentication codes at the end of the GOOSE message, as standardized by IEC 62351-6. With this measure, the sending IED is clearly identified and it becomes impossible to manipulate the GOOSE message content. Note that it is not necessary to encrypt the message to get these features. To deliver and maintain these authentication keys for each IED, a key management infrastructure is needed inside the substation. Because of this, these GOOSE security mechanisms have not gained widespread use, yet – but they will. The same applies to MMS and Role-based access control.

Encryption has not been mentioned, though it is often seen as the silver bullet for security. The IEC 62351 standard also provides encryption for GOOSE and MMS. However, in the substation environment, there are only a few applications imaginable where confidentiality of messages is important. If messages cannot be tampered with (integrity) and the originator can be verified (authentication) – which is fulfilled by using authentication in GOOSE and MMS, it is not necessary to encrypt the messages. One example where encryption could be necessary is if routable GOOSE (R-GOOSE) are transmitted over an unencrypted communication path. Encryption only provides additional CPU load on the IEDs, decreases GOOSE transmission time and impedes testing scenarios, but in most cases doesn’t provide additional security than authentication codes already provide. Encryption also makes a later analysis of traffic recordings difficult and it impedes monitoring approaches such as the ones described below.

Defense in depth
Most IEC 61850 substations built up until now have not implemented IEC 62351. Even in substations where GOOSE and with authentication codes are applied, infected devices in the network could still infect other devices or affect availability by disturbing the communication system. Therefore, most security frameworks recommend the usage of “Intrusion Detection Systems” (IDS), a well-known term from classic IT systems, to detect threats and malicious activity on the network. Such IDS are now becoming more common in the power system domain.

In an IEC 61850 substation, an IDS would be connected as depicted in the figure on the first page. Mirror ports on all relevant switches forward a copy of all network traffic to the IDS. The IDS inspects all network traffic communicated over these switches. To be able to analyze the most important traffic between the gateway and the IEDs, the IDS should, at a minimum, be connected to the switch next to the gateway and all other critical entry points into the network. The bay-level switches don’t usually need to be covered as typically only multicast traffic (GOOSE, Sampled Values) originates from there. To ensure that all unicast traffic in all network branches is analyzed, it is essential that all switches are mirrored into the IDS, which is not always possible if switch chips integrated into the IEDs are used.

However, IDS from classic IT are not suitable for the substation environment. While classic IT security is concerned with high-performance servers with millions of connections at the same time, substation IT security deals with devices with limited resources, custom operating systems, real-time demands, and specialized redundancy protocols. For example, a “denial-of-service” attack on an IED’s communication service often only requires 10 connections, such as 10 Ethernet packets, to be successful. This is simply because “denial-of-service” scenarios were not considered in the “good old days” when these devices and protocols were developed. Additionally, there are only a small number of known cyber attacks on substations, but even the first occurrence of a new attack could have severe consequences. Thus, a substation IDS must be able to detect attacks without any previous knowledge about what the attack might look like. This is a very different approach than that of a virus scanner, which has a list of virus signatures it looks for.

Learning-based systems
To be able to detect unknown attacks, many vendors use a “learning-phase” approach. Such systems look at frequency and timing of certain protocol markers to attempt to learn the usual behavior of the system. After the learning phase is complete, an alarm will be raised if one of the markers is significantly outside the expected range. This has the effect that false alarms are triggered for everything that did not occur during the learning phase, such as protection events, uncommon switching or automation actions, or routine maintenance and testing. Because these systems don’t understand the semantics of the protocols, the alarm messages are expressed in terms of technical protocol details. Hence, alarms can only be examined by an engineer skilled in IEC 61850 protocol details and familiar with IT network security. The engineer examining the alarm must also know about the operational situation to judge if certain IEC 61850 protocol events correspond to valid behavior. Therefore, a high number of false alarms occur for every substation, all of which require examination by highly skilled personnel. This often leads to alarms being ignored or alarms being discarded without investigation, and ultimately the IDS being switched off.

The Approach
For IEC 61850 substations, the whole automation system, including all devices, their data models, and their communication patterns is described in a standardized format – the SCL. System Configuration Description (SCD) files normally also contain information about primary assets and, for an ever-increasing number of substations, even the single-line diagram is present.

This information allows a different approach to be used for detecting intrusions: The monitoring system can create a full system model of the automation and power system and it can compare each and every packet on the network against the live system model. Even the variables contained in the communicated (GOOSE, MMS, SV) messages can be evaluated against the expectations derived from the system model. This process is possible without the need for a learning phase, just by configuration from SCL. This approach is implemented in the new functional security monitoring system StationGuard.

Functional Security Monitoring
In essence, very detailed functional monitoring is produced to detect cyber threats in the network. Because of the detail level of the verification, it is not only cybersecurity threats like malformed packets and disallowed control actions that are detected, but also communication failures, time synchronization problems, and consequently also (certain) equipment failures. If the single-line diagram is known to the system, and measurement values can be observed in MMS (or even through Sampled Values) communication, the possibilities of what can be verified are endless.

For example, for GOOSE alone there are 33 alarm codes available for things that could go wrong. These range from simple stNum/sqNum glitches (as explained above) to more complex issues, such as too long transmission times. The latter is detected by accurately measuring the difference between the EntryTime timestamp in the message and the arrival time at StationGuard. If this network transmission time is significantly longer than 3 ms for a “protection” GOOSE (referring to IEC 61850-5), it indicates a problem in the network or in the time synchronization.

What is done for MMS communication? From the system model (from the SCL) it is known which Logical Nodes control which primary assets. Thus, it can be distinguished between correct/incorrect, and critical/noncritical actions. Switching a circuit breaker and switching the IEC 61850 test mode use the same sequence in the MMS protocol (select-before-operate), but the effect in the substation is quite different. So, if the Test PC from Figure 1 switches the test mode on a relay this may be a legitimate action during maintenance, but it is most probably not legitimate that the Test PC operates a breaker. There will be a more in-depth look at this example in the following paragraphs.

Developed with PAC engineers
Research on this approach started in 2011. Spin-offs of this concept, the 24/7 functional supervision of SV, GOOSE and PTP time synchronization, have been available in a distributed and hybrid analysis device (OMICRON DANEO 400) since 2015. Triggered by this, we were approached by the Swiss distribution and generation operator CKW. They were familiar with the disadvantages of commercially available IDS and were looking for a more suitable solution for substations and one that is friendlier for protection, automation and control engineers. This led to a cooperation between the PAC engineers of CKW and the development team for our solution. It was intriguing to hear how they planned intrusion detection to be part of their future substation cybersecurity design. Meanwhile, feedback from many other utilities worldwide, as well as some proof-of-concept installations, found its way into our development.

In 2018, one of the first proof-of-concept installations was installed in a 110 kV CKW substation and has been running since then. Figure 2 shows the installation using the mobile hardware platform MBX1 at the bottom of the picture. In this setup, all traffic from the “core” switch was mirrored to StationGuard. This ensures that all the communication from the gateway to and from all IEDs is visible. Because remote maintenance connections also enter through that switch, all this traffic can also be inspected by StationGuard. Since GOOSE communication is multicast, and because the network setup allows it, all GOOSE from the IEDs in the substation bays are also visible to StationGuard.


Figure 2: Installation in CKW 110 kV substationAlert Display
Besides the avoidance of false alarms, it is also of vital importance that the alarm messages delivered are understandable to the engineers who are responsible for the operation of the protection, automation and network functions within the substation. This allows faster reaction times because often these alarms are triggered by engineers working in the substation (or from remote activities). Additionally, this allows security engineers and PAC engineers to collaborate when tracing events within a substation.

Figure 3 shows a screenshot of the graphical alarm display: The alarm is shown as an arrow from the active participant (Test PC) performing the prohibited action, and the “victim” of the action – a bay controller in bay Q01. Figure 4 reveals details about that alarm – a circuit breaker was operated (using an MMS control sequence), which is not allowed for a Test PC.

Figure 3: Graphical alarm display instead of event list. 

Figure 4: Details for Figure 3: Test PC attempting unauthorized control of circuit breaker.

Maintenance Mode
To avoid false alarms, routine testing and maintenance conditions must be included in the substation system model. This means that the testing and engineering equipment, including protection test sets, can be introduced into the system. In Figure 5 we see that maintenance was activated for Bay Q01. Now the Test PC from the example above can do more than before. There will be no alarm if the Test PC controls the IEC 61850 test or simulation mode of IED -Q1 in this bay. However, the same alarm as before will be triggered if the Test PC operates a breaker in that bay, since critical actions like this are not authorized for a Test PC. Of course, if company policies allow such actions, these rules can be modified.

Figure 5. Maintenance mode activated for bay Q01

As previously mentioned, no learning phase is required. The detection starts right from the time that the device is powered up and it cannot be turned off – for security reasons. Until the SCD file of the substation is loaded, all IEDs will be detected and presented as unknown devices. Once the SCD file is loaded, the IEDs will be indicated as known devices and the substation structure is assembled into a “zero-line” diagram, as it was introduced with StationScout. The configuration can also be prepared in the office and then installed on-site, one after the other, with fast commissioning. If not all IEDs were engineered into one file (these things happen), then additional IEDs can also be imported one by one. Once the import is done, the user can add roles such as “Test PC”, “Engineering PC”, etc. to any remaining unknown devices.

What happens in case of an alarm?
It is important to note that the StationGuard is purely passive, if an action is “not allowed” it will trigger an alarm. This alarm can be communicated to the Gateway/RTU and control center or to a separate system collecting security alerts – known as A Security Incident Event Management (SIEM) system. StationGuard does not actively react or interfere with the substation. Depending on the chosen hardware variant, user-definable binary outputs are available to be wired directly to the RTU. In this case, the alarm signalization happens without network communication and the alarms can be integrated into the normal SCADA signal list like any other hard-wired signal from the station.

Cybersecurity of the IDS
As we know from b-grade movies, burglars always attack the burglar alarm system first. So what about the security of this alarm system? An important aspect is that a stand-alone, secure hardware is used and not a virtual machine. Both hardware variants of StationGuard, the mobile (MBX1) and the 19”-variant for permanent installation (RBX1), have the same platform hardening. They both have a secure cryptoprocessor chip according to ISO/IEC 11889. This ensures that cryptographic keys are not stored on the flash storage but in a separate chip which is protected against tampering. By installing the OMICRON certificates on this chip during production, a secure, measured boot chain is created. This means that each step in the firmware bootup process verifies the signatures of the next module or driver to load. This makes sure that only software signed by OMICRON can be executed. The storage of the devices is encrypted with a key unique for that hardware and is protected inside the cryptochip. Because nobody (including OMICRON) knows this key, all data on the device will be lost when the hardware is replaced on repair. Many other mechanisms make sure that the processes on the device cannot be attacked or misused, so that the “defense in depth” approach is also applied deep into the software running on the device. Covering all these mechanisms would be a complete topic for another article.

Substations provide potential attack vectors for cyber attacks. If an attacker is able to influence one or more substations, this can have severe consequences for the grid. Therefore, effective cybersecurity measures must be implemented, not only in the control centers, but also in substations. For IEC 61850 substations, an approach for intrusion detection is available which provides a small number of false alarms and still low configuration overheads due to the power of the SCL. This system not only detects security threats, but also functional problems of IEC 61850 communication and of the IEDs are detected – which is also helpful in the FAT and SAT phase. Intrusion detection systems that display detected events in the language of protection, automation and control engineers have the advantage that PAC and security engineers can work together to find the cause of events.

15 09 19

Antenna Design for 5G Communications

7 Jun

With the rollout of the 5th generation mobile network around the corner, technology exploration is in full swing. The new 5G requirements (e.g. 1000x increase in capacity, 10x higher data rates, etc.) will create opportunities for diverse new applications, including automotive, healthcare, industrial and gaming. But to make these requirements technically feasible, higher communication frequencies are needed. For example, the 26 and 28 GHz frequency bands have been allocated for Europe and the USA respectively – more than 10x higher than typical 4G frequencies. Other advancement will include carrier aggregation to increase bandwidth and the use of massive MIMO antenna arrays to separate users through beamforming and spatial multiplexing.

Driving Innovation Through Simulation

The combination of these technology developments will create new challenges that impact design methodologies applied to mobile and base station antennas currently. Higher gain antennas will be needed to sustain communications in the millimeter wavelength band due to the increase in propagation losses. While this can be achieved by using multi-element antenna arrays, it comes at the cost of increased design complexity, reduced beamwidth and sophisticated feed circuits.

Simulation will pave the way to innovate these new antenna designs through rigorous optimization and tradeoff analysis. Altair’s FEKO™ is a comprehensive electromagnetic simulation suite ideal for these type of designs: offering MoM, FEM and FDTD solvers for preliminary antenna simulations, and specialized tools for efficient simulation of large array antennas.

Mobile Devices

In a mobile phone, antenna real estate is typically a very limited commodity, and in most cases, a tradeoff between antenna size and performance is made. In the millimeter band the antenna footprint will be much smaller, and optimization of the antenna geometry will ensure the best antenna performance is achieved for the space that is allocated, also for higher order MIMO configurations.

At these frequencies, the mobile device is also tens of wavelengths in size and the antenna integration process now becomes more like an antenna placement problem – an area where FEKO is well known to excel. When considering MIMO strategies, it is also easier to achieve good isolation between the MIMO elements, due to larger spatial separation that can be achieved at higher frequencies. Similarly, it is more straightforward to achieve good pattern diversity strategies.



Base Station

FEKO’s high performance solvers and specialized toolsets are well suited for the simulation massive MIMO antenna arrays for 5G base stations. During the design of these arrays, a 2×2 subsection can be optimized to achieve good matching, maximize gain and minimize isolation with neighboring elements –a very efficient approach to minimize nearest neighbor coupling. The design can then be extrapolated up to the large array configurations for final analysis. Farming of the optimization tasks enables these multi-variable and multi-goal to be solved in only a few hours. Analysis of the full array geometry can be efficiently solved with FEKO’s FDTD or MLFMM method: while FDTD is extremely efficient (1.5 hrs for 16×16 planar array), MLFMM might also be a good choice depending on the specific antenna geometry.



The 5G Channel and Network Deployment

The mobile and base station antenna patterns that are simulated in FEKO, can used in WinProp™ for high-level system analysis of the 5G radio network coverage and to determine channel statistics for urban, rural and indoor scenarios.



WinProp is already extensively used for 4G/LTE network planning. However, the use cases for 5G networks will be even more relevant largely due to the different factors that occur in the millimeter band. These include higher path loss from atmospheric absorption and rainfall, minimal penetration into walls and stronger effects due to surface roughness.

In addition to being able to calculate the angular and delay spread, WinProp also provides a platform to analyze and compare the performance of different MIMO configurations while taking beamforming into account.


The Road to 5G

While some of the challenges that lie ahead to meet the 5G requirements may still seem daunting, simulation can already be used today to develop understanding and explore innovative solutions. FEKO offers comprehensive solutions for device and base station antenna design, while WinProp will determine the requirements for successful network deployment.



Comparing the mobile data networks of Europe in OpenSignal’s newest report

18 Aug

Today, OpenSignal released its new Global State of Mobile Networks report, our first worldwide report that looks beyond 4G technology to examine the overall mobile data prowess of nearly 100 different countries. While you can see the overall conclusions and analysis in the report itself, we’re also drilling down to specific regions in a short series of blog posts. Today we’re starting with Europe.

The chart below shows how 33 European countries stack up in mobile data performance, plotting combined 3G and 4G availability on the vertical axis and average 3G/4G speed on the horizontal axis.

3G/4G speed vs. 3G/4G availability

3G/4G speed vs. 3G/4G availability

Europe does quite well in general in both speed availability, reflecting not only their investments in LTE but the mature state of their LTE infrastructures. Most of them are clustered in the upper central portion of the chart with speeds between 10 and 20 Mbps and high levels of mobile data signal availability. The vast majority of European users can latch onto a 3G or better signal more 80% of the time, according to our data.

Outside of that main cluster, we do see clumps of countries in similar stages of development. We find several Eastern European countries that haven’t quite caught up with the rest of the region in either speed or availability (sometimes both), though Germany falls in the underperforming category as well. Being a former member of the eastern bloc isn’t always indicative of poorer mobile data performance, though. Both Lithuania and Hungary are well to the right of Europe’s main cluster, joining the Nordic states and the Netherlands in an exclusive club of outperformers. These are the rare countries that are able to offer a consistent mobile data connection greater than 20 Mbps.

3G signals are plentiful around the world

3G has definitely taken hold in most countries. On the 95 countries in our sample, 93 of them had 3G or better signal availability more than half the time, while the vast majority had availability greater than 75%, according to our data.

Big differences remain in average consumer data speeds

Though 3G or 4G connections may be the norm, there are some sizable gaps country-to-country in our overall speed metric, which measures the average download performance across all networks. South Korea had the fastest overall speed of 41.3 Mbps, while the slowest average we measured was 2.2 Mbps in Afghanistan.

The dominant connection type is (surprise!) Wifi

We found high levels of mobile Wifi connections both in countries where mobile broadband is ubiquitous and in countries where mobile data infrastructure is more limited. The most mobile-Wifi-hungry country in the world was the Netherlands, where Wifi accounted for 70% of all of the smartphone connections we measured.

LTE development patterns are clearly emerging

When we correlated overall speeds with 3G/4G availability, we found distinct clusters of countries in similar stages of mobile development. Examining 3G and 4G together paints a much clearer picture of a country’s network progress than measuring 4G alone.


The End of the Private Enterprise Network

16 Aug

The network is the last thing that IT fully controls within the enterprise and consumes 12-15% of the enterprise technology budget. Compute, storage and applications are moving to the cloud with its elastic, pay for what is used, model. Users are going mobile, working from anywhere. Networking will be the last thing that is moved to the cloud, but this too will happen.

Users get frustrated with the enterprise network because it is slower to work in the office than when they work from home. CIO’s wonder why they pay 20x more for enterprise bandwidth than what they pay as a consumer. Business leaders are also frustrated with the enterprise network because it is slowing down their digital transformation projects.

Enterprise networks are inherently slower, less agile, less secure, and more expensive because of:

  1. Backhauling – Sending all Internet destined traffic back to a data center before going out to the Internet. 80% of enterprise branch office traffic is Internet destined and the backhauling is both expensive and slows down cloud based applications. Mobile device managers also backhaul cellular data traffic, causing the same problem.
  2. Legacy business models – Buying upfront tons of equipment (routers, firewalls, load balancers, network optimizers, intrusion detection) and signing multi-year contracts with 1-2 network service providers.
  3. ACL hell – Access Control Lists are used by network equipment to define on every interface where packets can and cannot go. This manual process can lead to thousands of rules and spirals out of control with no one understanding why a rule put in 3 years ago still applies. Also, routers are not able to report on which ACLs are used. Every network change requires new ACLs, which can break existing applications, making networks very complex and fragile.
  4. Perimeter Security – The assumption that a private network is more secure has not proven true as the many hacks that have been published and the greater frequency in which they are occurring. A zero trust model is required to provide end-to-end security.

Software Defined Wide Area Networks (SD-WANs) are a step towards making networks faster, more agile, and lower costs. SD-WANs utilize broadband Internet to the branch office and provide a security stack at the edge of the network to minimize backhauling and cheaper bandwidth than MPLS. SD-WANs use centralized controllers and IPsec or GRE tunnels to create an overlay network to mask the underlying network complexity. This is why the SD-WAN market is going to grow from 500M this year to 6B by 2020.

But, SD-WANs are just a step towards the Next Generation WAN (NG-WAN) which will be managed by cloud providers through Network as a Service (NaaS). Microsoft, Google, and other large Cloud Service Providers (CSPs) are becoming network operators. Gartner reports that 50% of cloud implementations have business impacting problems due to the network. CSPs realize that if they are going to provide a Quality of Experience (QoE) for their applications, that they need to have greater control of connecting their users.

To achieve complete end to end control of business IT computing and incent migration to cloud services, CSPs will offer secure seamless networking solutions to connect from customer on-premises servers to in-cloud-based resources. The next generation networks will leverage broadband Internet connectivity and high speed optical and Ethernet networks that are inter-connected at the carrier neutral collocations where the CSP’s reside. On the premises will be white box switches and wireless local area networks connected to a very intelligent router and security stack that can dynamically establish direct, secure sessions between application services and users.

This can be done at a fraction of the cost because the CSPs already possess significant technical resources in networking and they have different business models than the traditional Network Service Providers (NSPs). CSPs over time will marginalize existing NSPs and shed the complexity, that inhibits broader migration to cloud-based services.

The market for enterprise networking will go through a radical shakeout and will become commoditized. White box/brite box providers that develop the appropriate partnerships will see new opportunities. Winners will include low cost access and transport service providers along with existing and new network equipment providers bold enough to morph into a volume player for a low margin business.

The best lens into the IT future is to watch what start-up companies are doing. These companies do not have any legacy baggage and adopt the latest and greatest technology and solutions. Few start-ups are creating their own private networks. AirBnB and Uber are examples of companies without a private MPLS WAN.

This is a paradigm shift for the enterprise to go to the 1,000 plus fiber networks and Internet Service Providers (ISPs) that the cloud providers use, versus bringing 1-2 NSPs & ISPs into the enterprise.

The End of the Private Enterprise Network


5G Network Architecture 5G Network Architecture – A High-Level Perspective

27 Jul



  • A Cloud-Native 5G Architecture is Key
  • to Enabling Diversified Service Requirements
  • 5G Will Enrich the Telecommunication Ecosystem
    • The Driving Force Behind Network Architecture Transformation
    • The Service-Driven 5G Architecture
  • End-to-End Network Slicing for Multiple
  • Industries Based on One Physical Infrastructure
  • Reconstructing the RAN with Cloud
  • 1 Multi-Connectivity Is Key to High Speed and Reliability
  • 2 MCE
  • Cloud-Native New Core Architecture
  • 1 Control and User Plane Separation Simplifies the Core Network
  • 2 Flexible Network Components Satisfy Various Service Requirements
  • 3 Unified Database Management
  • Self-Service Agile Operation
  • Conclusion:
  • Cloud-Native Architecture is the Foundation of 5G Innovation

Download: 5G-Nework-Architecture-Whitepaper-en

LTE Network Architecture

3 Mar

The high-level network architecture of LTE is comprised of following three main components:

  • The User Equipment (UE).
  • The Evolved UMTS Terrestrial Radio Access Network (E-UTRAN).
  • The Evolved Packet Core (EPC).

The evolved packet core communicates with packet data networks in the outside world such as the internet, private corporate networks or the IP multimedia subsystem. The interfaces between the different parts of the system are denoted Uu, S1 and SGi as shown below:
LTE Architecture

The User Equipment (UE)

The internal architecture of the user equipment for LTE is identical to the one used by UMTS and GSM which is actually a Mobile Equipment (ME). The mobile equipment comprised of the following important modules:

  • Mobile Termination (MT) : This handles all the communication functions.
  • Terminal Equipment (TE) : This terminates the data streams.
  • Universal Integrated Circuit Card (UICC) : This is also known as the SIM card for LTE equipments. It runs an application known as the Universal Subscriber Identity Module (USIM).

A USIM stores user-specific data very similar to 3G SIM card. This keeps information about the user’s phone number, home network identity and security keys etc.

The E-UTRAN (The access network)

The architecture of evolved UMTS Terrestrial Radio Access Network (E-UTRAN) has been illustrated below.
LTE E-UTRANThe E-UTRAN handles the radio communications between the mobile and the evolved packet core and just has one component, the evolved base stations, called eNodeB or eNB. Each eNB is a base station that controls the mobiles in one or more cells. The base station that is communicating with a mobile is known as its serving eNB.
LTE Mobile communicates with just one base station and one cell at a time and there are following two main functions supported by eNB:

  • The eBN sends and receives radio transmissions to all the mobiles using the analogue and digital signal processing functions of the LTE air interface.
  • The eNB controls the low-level operation of all its mobiles, by sending them signalling messages such as handover commands.

Each eBN connects with the EPC by means of the S1 interface and it can also be connected to nearby base stations by the X2 interface, which is mainly used for signalling and packet forwarding during handover.
A home eNB (HeNB) is a base station that has been purchased by a user to provide femtocell coverage within the home. A home eNB belongs to a closed subscriber group (CSG) and can only be accessed by mobiles with a USIM that also belongs to the closed subscriber group.

The Evolved Packet Core (EPC) (The core network)

The architecture of Evolved Packet Core (EPC) has been illustrated below. There are few more components which have not been shown in the diagram to keep it simple. These components are like the Earthquake and Tsunami Warning System (ETWS), the Equipment Identity Register (EIR) and Policy Control and Charging Rules Function (PCRF).
LTE EPCBelow is a brief description of each of the components shown in the above architecture:

  • The Home Subscriber Server (HSS) component has been carried forward from UMTS and GSM and is a central database that contains information about all the network operator’s subscribers.
  • The Packet Data Network (PDN) Gateway (P-GW) communicates with the outside world ie. packet data networks PDN, using SGi interface. Each packet data network is identified by an access point name (APN). The PDN gateway has the same role as the GPRS support node (GGSN) and the serving GPRS support node (SGSN) with UMTS and GSM.
  • The serving gateway (S-GW) acts as a router, and forwards data between the base station and the PDN gateway.
  • The mobility management entity (MME) controls the high-level operation of the mobile by means of signalling messages and Home Subscriber Server (HSS).
  • The Policy Control and Charging Rules Function (PCRF) is a component which is not shown in the above diagram but it is responsible for policy control decision-making, as well as for controlling the flow-based charging functionalities in the Policy Control Enforcement Function (PCEF), which resides in the P-GW.

The interface between the serving and PDN gateways is known as S5/S8. This has two slightly different implementations, namely S5 if the two devices are in the same network, and S8 if they are in different networks.

Functional split between the E-UTRAN and the EPC

Following diagram shows the functional split between the E-UTRAN and the EPC for an LTE network:

2G/3G Versus LTE

Following table compares various important Network Elements & Signaling protocols used in 2G/3G abd LTE.

DiameterGTPc-v0 and v1 GTPc-v2


Cisco Sets Digital Network Architecture as its Platform of the Future

3 Mar

Cisco unveiled its Digital Network Architecture (DNA) for transforming business with the power of analytics driven by programmable networks, cloud applications, open APIs, and virtualization.  The Cisco DNA aims to extend the company’s data center-based, policy-driven Application Centric Infrastructure (ACI) technology throughout the entire network: from campus to branch, wired to wireless, core to edge.

Cisco DNA is built on five guiding principles:

  • Virtualize everything to give organizations freedom of choice to run any service anywhere, independent of the underlying platform – physical or virtual, on premise or in the cloud.
  • Designed for automation to make networks and services on those networks easy to deploy, manage and maintain – fundamentally changing the approach to network management.
  • Pervasive analytics to provide insights on the operation of the network, IT infrastructure and the business – information that only the network can provide.
  • Service management delivered from the cloud to unify policy and orchestration across the network – enabling the agility of cloud with the security and control of on premises solutions.
  • Open, extensible and programmable at every layer – Integrating Cisco and 3rd party technology, open API’s and a developer platform, to support a rich ecosystem of network-enabled applications.

“The digital network is the platform for digital business,” said Rob Soderbery, SVP for Enterprise Products and Solutions, Cisco.  “Cisco DNA brings together virtualization, automation, analytics, cloud and programmability to build that platform.  The acronym for the Digital Networking Architecture – DNA – isn’t an accident. We’re fundamentally changing the DNA of networking technology.”

The first deliverables of Cisco DNA include:

DNA Automation:  APIC-Enterprise Module (APIC EM) Platform

  • APIC-EM Platform:  A new version of Cisco’s enterprise controller has been released. Cisco claims 100+ customer deployments running up to 4000 devices from a single instance.  The company is adding automation software that removes the need for staging for pre-configuration or truck roll-outs to remote locations. The Plug and Play agent sits on Cisco routers and switches and talks directly to the network controller. A new EasyQoS service enables the network to dynamically update network wide QoS settings based on application policy.
  • Cisco Intelligent WAN Automation Services: This service automates IWAN deployment and management, providing greater WAN deployment flexibility and allowing IT to quickly configure and deploy a full-service branch office with just 10 clicks.  IWAN automation eliminates configuration tasks for advanced networking features, and automatically enables Cisco best practices, application prioritization, path selection and caching to improve the user experience.
  • DNA Virtualization:  Evolved IOS-XE is a network operating system optimized for programmability, controller-based automation, and serviceability. The new OS provides open model-driven APIs for third party application development, software-defined management, application hosting, edge computing and abstraction from the physical infrastructure to enable virtualization.   It supports the Cisco Catalyst 3850/3650, ASR 1000 and ISR 4000 today, and will continue to be expanded across the Enterprise Network portfolio.

    Evolved Cisco IOS XE includes Enterprise Network Function Virtualization (Enterprise NFV) that decouples hardware from software and gives enterprises the freedom of choice to run any feature anywhere. This solution includes the full software stack – virtualization infrastructure software; virtualized network functions (VNFs) like routing, firewall, WAN Optimization, and WLAN Controller; and orchestration services – to enable branch office service virtualization.

  • DNA Cloud Service Management:  CMX Cloud provides business insights and personalized engagement using location and presence information from Cisco wireless infrastructure.  With CMX Cloud enterprises can provide easy Wi-Fi onboarding, gain access to aggregate customer behavior data, and improve customer engagement.

Things that use Curve25519

14 Feb

Here’s a list of protocols and software that use or support the superfast, super secure Curve25519 ECDH function from Dan Bernstein. Note that Curve25519 ECDH should be referred to as X25519.

You may also be interested in this list of Ed25519 deployment.

This page is divided by Protocols, Networks, Operating Systems, Software, TLS Libraries, Libraries,Miscellaneous, Timeline notes, and Support coming soon.


  • DNS
    • DNSCurve — encrypted DNS between a resolver and authoritative server
    • DNSCrypt — encrypted DNS between a client and a resolver
  • Transport
    • CurveCP — a secure transport protocol
    • QUIC — a secure transport protocol
    • ZeroMQ — a secure transport protocol
    • Nitro — a library for painlessly writing scalable, fast, and secure message-passing network applications
    • lodp — Lightweight Obfuscated Datagram Protocol
    • RAET — (Reliable Asynchronous Event Transport) Protocol
    • SSH, thanks to the non-standard key exchange from the libssh team, adopted by OpenSSH and tinyssh
  • TLS
    • Nettle is the crypto library underneath GnuTLS
    • BoringSSL from Google
    • Other libraries are coming!
  • IPsec
    • OpenIKED — IKEv2 daemon which supports non-standard Curve25519
  • ZRTP
  • Other
    • TextSecure — encrypted messaging protocol derivative of OTR Messaging
    • Pond — forward secure, asynchronous messaging for the discerning
    • ZeroTier — Create flat virtual Ethernet networks of almost unlimited size
    • telehash — encrypted mesh protocol
    • bubblestorm — P2P group organization protocol
    • Apple AirPlay — stream content to HDTV/speakers


  • Tor — The Onion Router anonymity network
  • GNUnet — a framework for secure peer-to-peer networking that does not use any centralized or otherwise trusted services
  • URC — an IRC style, private, security aware, open source project
  • Serval — Mesh telecommunications
  • cjdns — encrypted ipv6 mesh networking
    • Plus the Enigmabox — a Hardware cjdns router

Operating Systems

  • OpenBSD — used in OpenSSH, OpenIKED, and in CVS over SSH
  • Apple iOS — the operating system used in the iPhone, iPad, and iPod Touch
  • Android — ships with Chrome, which uses Curve25519 in QUIC
  • Cyanogenmod — version 11+ ships with TextSecure
  • All operating systems that ship with OpenSSH 6.5+ from the OpenBSD Project


  • DNS
  • Web browsers
  • CurveCP related
    • CurveProtect — securing major protocols with CurveCP. Also supports DNSCurve.
    • qremote — an experimental drop-in replacement for qmail’s qmail-remote with CurveCP support
    • curvetun — a lightweight curve25519-based IP tunnel
    • spiral-swarm — easy local file transfer with curvecp [ author recommends another project ]
    • QuickTun — “probably the simplest VPN tunnel software ever”
    • jeremywohl-curvecp — “A Go CurveCP implementation I was sandboxing; non-functional.”
    • curvecp.go — Go implementation of the CurveCP protocol
    • curvecp — Automatically exported from
    • urcd — the most private, secure, open source, “Internet Relay Chat” style chat network
  • MinimaLT related (all Pre-Alpha, not production ready, please contribute!)
    • The MinimaLT authors will soon release beta code. But some people are so excited about the protocol that they’ve written approximations based on published descriptions of it. Since I’m excited about MinimaLT as well, and since it shows serious public interest, I’m listing the following here.
    • mltpipepy — spiped style tunnel for the MinimaLT protocol implemented in Python 3
    • nimbus-network-minimalt — C implementation of MinimaLT
    • MinimaLT-experimental — an approximation of the MinimaLT protocol, in javascript
    • safeweb — Proposition of a faster and more secure Web (MinimaLT + DNSNMC)
    • Github lists something called “minimalt-go” by nimbus-network. It’s not MinimaLT! At a glance it uses the NSA/NIST curve P-256, and AES. Not X25519 and Salsa20 like MinimaLT.
  • Tox Software
    • Tox — Free, secure, Skype alternative
    • toxcore — an easy to use, all-in-one communication platform
    • uTox — Lightweight Tox client
    • qTox — Powerful Tox client that follows the Tox design guidelines
    • Toxy — Metro-style tox client for Windows
    • CzeTox — School project: Tox client in Qt (alpha code)
    • OneTox — Tox client for the Universal Windows Platform
    • toxcore-vs — All necessary libs to build static toxcore using Visual Studio 2013
    • toxic — CLI Tox client
  • SSH Software
    • OpenSSH — Secure Shell from the OpenBSD project
    • TinySSH — a small SSH server with state-of-the-art cryptography
    • Win32-OpenSSH — Win32 port of OpenSSH
    • asyncssh — an asynchronous SSH2 client and server atop asyncio
    • pssht — SSH server written in PHP
    • SmartFTP — an FTP, SSH, SFTP client
    • Dropbear — an SSH server and client
    • Tera Term — SSH client for Windows
  • Other Software
    • Tor — The Onion Router
    • TextSecure — secure text messaging
    • OpenIKED — IKEv2 daemon for IPsec, from the OpenBSD project
    • WhatsAppnot all platforms implement X25519! To be safe, use TextSecure
    • Signal Desktop — Signal Private Messenger for the Desktop
    • Signal — Free, world-wide, private messaging and phone calls for iPhone
    • textsecure-go — TextSecure client package for Go
    • tweetnacl-tools — Tools for using TweetNaCl
    • haskell-tor — A Haskell implementation of the Tor protocol
    • Secrete — ECIES implementation with Curve25519
    • Tinfoil Chat NaCl — a high assurance encryption plugin for Pidgin IM
    • vcrypt — Toolkit for multi-factor, multi-role encryption
    • KinomaJS — A JavaScript runtime optimized for the applications that power IoT devices
    • srlog2 — Secure Remote Log Transmission System
    • encryptify — encryptify encrypts files
    • gobox — Trivial CLI wrapper around go.crypto/nacl/box
    • zkm — Zero Knowledge Messaging
    • qabel-core — Implementation of Qabel-Core in Java
    • Rubinius Language Platform — a modern language platform that supports a number of programming languages
    • servertail — quickly and easily see real time output of log files on your servers
    • cryptomirror — explores ways to make crypto user-friendly in non-crypto friendly environments
    • couch-box — Asymmetric encrypted CouchDB documents, powered by NaCl’s curve25519-xsalsa20-poly1305
    • saltcellar — libsodium based file encryption
    • SQRL — Secure Quick Reliable Login
    • curve-keygen — a utility to generate Curve25519 keypairs
    • confidential-publishing — Code for “A decentralized approach to publish confidential data”
    • cryptutils — Various crypto utilties based on a common NaCl/Ed25519 core
    • SMSSecure — fork of TextSecure which adds encrypted SMS support
    • gr-nacl — GNU Radio module for data encryption using NaCl library
    • up — sending a file from one computer to another using the nacl library
    • quicbench — HTTP/QUIC load test and benchmark tool
    • session25519 — Derive curve25519 key pair from email/password via scrypt
    • Bleep — Private instant messaging via secure, distributed technology
    • pcp — Pretty Curved Privacy
    • opake — Messaging with in-browser encryption using curve25519
    • CurvedSalsa — encrypt/decrypt files with Salsa20 & Curve25519
    • asignify — Yet another signify tool
    • nymphemeral — an ephemeral nymserver GUI client
    • hs-noise — encrypted networking in Haskell
    • CPGB — Curve Privacy Guard B, a secure replacement for GPG using ECC
    • SigmaVPN — simple, light-weight and modular VPN software for UNIX systems
    • fastd — Fast and Secure Tunneling Daemon
    • Simply Good Privacy — PGP-like system without web of trust
    • PoSH-Sodium — Powershell module to wrap libsodium-net methods
    • midgetpack — a multiplatform secure ELF packer
    • dhbitty — a small public key encryption program written in C
    • Threema — encrypted messaging app (closed source)
    • tappet — a tiny encrypted UDP tunnel using TweetNaCl
    • Osteria — secure point-to-point messenger
    • mcrypt — Message Crypto – Encrypt and sign individual messages
    • chdkripto — CHDK firmware – crypto modules (work in progress)
    • CurveLock — message and file encryption for Windows
    • Securecom Text — a messaging app for easy private communication with friends
    • srndv2 — some random news daemon (version 2)
    • GoVPN — simple high-performance secure VPN using DH-EKE
    • Core Secret — Secure secret sharing between Bluetooth Low Energy peers on iOS
    • AxolotlKit — a free implementation of the Axolotl protocol
    • pyaxo — A python implementation of the Axolotl ratchet protocol
    • reop — reasonable expectation of privacy
    • SUPERCOP — a cryptographic benchmarking suite

TLS Libraries

  • BoringSSL
  • Others coming soon, which is next?!



  • Dan Bernstein: “An attacker who spends a billion dollars on special-purpose chips to attack Curve25519, using the best attacks available today, has about 1 chance in 1000000000000000000000000000 of breaking Curve25519 after a year of computation.”
  • Dmitry Chestnykh: “You can write a program to generate Curve25519 private key faster than PGP generates its private key.”
  • Adam Langley: “Of the concrete implementations of Diffie-Hellman, curve25519 is the fastest, common one. There are some faster primitives in eBACS, but the ones that are significantly faster are also significantly weaker.”
  • Matthew Green: “Any potential ‘up my sleeve’ number should be looked at with derision and thoroughly examined (Schneier thinks that the suggested NIST ECC curves are probably compromised by NSA using ‘up my sleeve’ constants). This is why I think we all should embrace DJB’s curve25519.”
  • Frederic Jacobs: “It’s incredible to realize that the TextSecure protocol enabled the largest end-to-end encrypted messaging deployement in history.”
  • GnuPG: “For many people the NIST and also the Brainpool curves have an doubtful origin and thus the plan for GnuPG is to use Bernstein’s Curve 25519 as default. GnuPG 2.1.0 already comes with support for signing keys using the Ed25519 variant of this curve. This has not yet been standardized by the IETF (i.e. there is no RFC) but we won’t wait any longer and go ahead using the proposed format for this signing algorithm.”
  • Ian Grigg: “In the past, things like TLS, PGP, IPSec and others encouraged you to slice and dice the various algorithms as a sort of alphabet soup mix. Disaster. What we got for that favour was code bloat, insecurity at the edges, continual arguments as to what is good & bad, focus on numbers & acronyms, distraction from user security, entire projects that rate your skills in cryptoscrabble, committeeitus, upgrade nightmares, pontification … Cryptoplumbing shouldn’t be like eating spagetti soup with a toothpick. There should be One Cipher Suite and that should do for everyone, everytime. There should be no way for users to stuff things up by tweaking a dial they read about in some slashdot tweakabit article while on the train to work… Picking curve25519xsalsa20poly1305 is good enough for that One True CipherSuite motive alone… It’s an innovation! Adopt it.”
  • wolfSSL: “Curve25519 so far is destroying the key agreement and generation benchmarks of previous curves, putting up numbers for both key agreement and generation that are on average 86 percent faster than those of NIST curves.”
  • Adam Langley: “Current ECDSA deployments involve an ECDSA key in an X.509 certificate and ephemeral, ECDHE keys being generated by the server as needed. These ephemeral keys are signed by the ECDSA key. A similar design would have an Ed25519 key in the X.509 certificate and curve25519 used for ECDHE. I don’t believe there’s anything needed to get that working save for switching out the algorithms.”

Timeline notes

X25519 support coming soon!

  • MinimaLT — A super fast, super secure transport protocol
  • TLS — Transport Layer Security
  • Ethos — An operating system to make it far easier to write applications that withstand attack
  • wolfSSL — for use in TLS
  • Microsoft TLS
  • dnsdist — a highly DNS-, DoS- and abuse-aware loadbalancer (adding DNSCrypt support)
  • curvecp-javascript — CurveCP protocol implementation in pure Javascript
  • php71_crypto — Pluggable Cryptography Interface for PHP 7.1
  • jc_curve25519 — Javacard implementation of Curve25519 (prototype, work-in-progress)
  • ConnectBot — the first SSH client for Android
  • sshlib — ConnectBot’s SSH library
  • Cyberduck — Libre FTP, SFTP, WebDAV, S3, Azure & OpenStack Swift browser for Mac and Windows
  • djbdnscurve6 — dnscache with DNSCurve & IPv6 support
  • JackPair — secure your voice phone calls against wiretapping
  • PuTTY — A Free Telnet/SSH Client
  • cjdrs — cjdns implementation in Rust
  • freepass — “TODO SQRL”
  • molch — An implementation of the axolotl ratchet based on libsodium
  • libsodium-laravel — Laravel integration for lib sodium
  • mute — secure messaging (currently in alpha release)
  • Tahoe-LAFS — Free and Open cloud storage system
  • Cloudflare“once QUIC makes the move from experimental to beta we’ll be sure to make it available for our customers.”
  • gospdyquic — SPDY/QUIC support for Go
  • Tox.NET — WIP reimplementation of Tox in C#
  • opt-cryptobox — Optimized cryptobox self-contained library
  • goquic — QUIC support for Go
  • SC4 — Strong Crypto for Mere Mortals
  • End-To-End — a Chrome extension that helps you encrypt, decrypt, digital sign, and verify signed messages within the browser using OpenPGP
  • Yahoo End-To-End — Use OpenPGP encryption in Yahoo mail.
  • TextSecure-Browser — TextSecure as a Chrome Extension
  • curve_tun — TCP tunnels secured by Curve25519
  • Dust — A Blocking-Resistant Internet Transport Protocol
  • Twisted Python SSH — event-driven Python
  • pouch-box — Asymmetric encrypted PouchDB, powered by NaCl’s curve25519-xsalsa20-poly1305
  • Blight — a Tox client written in Racket that utilizes libtoxcore-racket
  • GnuPG — end-to-end encrypted email. Note: Alternatives like reop support Curve25519 now.
  • Noise — a secure transport protocol.
  • BitTorrent Live — uses crypto_box from NaCl
  • strongSwan — IPsec for Linux
  • TextSecureKit — a boilerplate for Mac & iOS apps
  • libopenssh — turn OpenSSH into a library


Software-Defined Storage: The 2016 Outlook

1 Feb

Interest in SDS is growing as companies look for alternatives to high-priced storage drives.

Software-defined networking is beginning to take off, but what’s happening with software-defined storage? We are well into the hype phase, with everything from backup managers to disk drives being described as “software-defined” and we are perhaps just beginning to see the first real SDS products emerge. That’s a long way from mainstream — or is it?

Despite all of the hype, startups have been developing new solutions and SDS may be closer to becoming a reality than you think. Let’s look at why that is. Mr. Gillette would recognize today’s storage business in an instant. Razors and razor-blades or appliances and drives — they’re essentially the same business model. The major vendors have built a business where commodity drives are marked up enormously, while ensuring that cheap drives can’t be used in their arrays by getting unique identifiers added to the drive firmware.

But the cloud and other trends are bursting the bubble and paving the way for software-defined storage. Cloud providers like Google don’t buy specialized drives;  everything COTS, with the result that the mega-CSPs enjoy $30 per terabyte hard drives while many businesses are locked into $300+ drives.

Looking at some numbers, we see a $190 list price 3 TB SAS drive marked up to $4,215 by EMC, $1,856 by NetApp and “only” $532 by Dell. But that’s only part of the story. Google uses many cheap SATA drives, with solid-state drives for fast work; a fast terabyte SSD/flash card likely costs Google around $500. List price for an 800 GB SAS SSD is $739. EMC sells that for $14,435 — a 20X markup!

So what does all of this have to do with software-defined storage? We now realize that there are cheaper alternatives that will allow cost containment of the expected explosion in capacity requirements. The problem has been getting to them. Hardware isn’t enough on its own; we need good software, and this is where SDS becomes important.

To get commodity prices on drives, the appliance has to be free of any proprietary lock-in. That precludes the traditional vendors and means that alternative sources for appliances are needed. These can be COTS units from the same companies that supply AWS, Google and Azure: The Chinese ODMs, such as Supermicro, Lenovo, and Quanta. Such units are high quality  — the CSPs assure that by buying in millions of units — and very inexpensive compared with the traditional storage array or appliance.

The next, and maybe most important issue, is finding software to run the appliances. Some software vendors such as Caringo and DataCore sell software that runs on COTS servers. Even better, open-source efforts such as Ceph and OpenStack Swift and Cinder are creating viable strong solutions for point appliances.

These software tools make deployment of a low-cost, COTS-based storage farm feasible and attractive, but are they SDS? The concept behind SDS is deceptively simple: Take the complicated data services that sit on top of storage and move them from the appliances to virtual machines sitting in servers. This allows right-sizing of the storage services for workload variation and also, incidentally, makes services compete with each other for market share, bringing prices down.

That’s the theory. Ceph is on the edge of SDS-compatibility. It is Lego-like and could be reconstructed to allow service abstraction. This would benefit the object/file/block universal storage software tremendously since missing features such as encryption, compression and deduplication could be integrate into the dataflow. With rewrites planned for the OSD storage node software in Ceph, this would be a great time to consider its SDS credentials more closely.

DataCore and FalconStor have software products that meet the definition of SDS and provide an inexpensive way to feature up boxes. These still move data through the service instance, which is a weakness shared with the current Ceph approach. Primary Data’s DataSphere  attempts code that is more like asynchronous pooling, where the producer of data talks to the service and organizes metadata and chunk addressing and then communicates directly with a set of storage devices to read or write data. In another development, Nutanix is considering selling its software as a subscription service without a hardware appliance, while partnering with Dell, Lenovo and SuperMicro to put that code on their platforms.

We can expect the major storage vendors to react to the threat of SDS by introducing their own software products. Whether these are really SDS and whether they free the buyer from vendor lock-in on drives remains to be seen.

SDS is still in its early stages, but the signs of aggressive growth seem evident. Interest is high and some estimate that more than 70%  of companies will try the approach, if not deploy it, in 2016. With intense pressure on IT budgets and a need to grow capacity dramatically looming, SDS may be the answer.


Interference Management

11 Jan

A. Interference Management with Delayed and Distributed CSIT

Channel state information at the transmitter (CSIT) plays an important role in interference management in wireless systems. Interference networks with global and instantaneous CSIT provide a great improvement of performance. In practice, however, obtaining global and instantaneous CSIT for transmitter cooperation is especially challenging, when the transmitters are distributed and the mobility of wireless nodes increases. In an extreme case where the channel coherence time is shorter than the CSI feedback delay, it is infeasible to acquire instantaneous CSIT in wireless systems. Obtaining global knowledge of CSIT is another obstacle for realizing transmitter cooperation when the backhaul or feedback link capacity is very limited for CSIT sharing between the distributed transmitters. Therefore, one of fundamental questions is that it still possible to obtain benefits in increasing the scaling law of the rate, i.e., degress-of-freedom (DoF), for interference networks under these two practical constraints?

Motivated by this question, I have proposed interference alignment algorithms exploiting local and moderately-delayed CSIT. The proposed method is a structured space-time repetition transmission technique that exploits both current and outdated CSIT jointly to align interference signals at unintended receivers in a distributed way. With this algorithm, they characterize trade-off regions between the sum of degrees of freedom (sum-DoF) and feedback delay in vector broadcast channels, the X channels, and a three-user interference channel to reveal the impact on how the CSI feedback delay affects the sum-DoF of the interference networks.

The key finding from this work is that distributed and moderately-delayed CSIT is useful to obtain strictly better the sum-DoF over the case of no CSI at the transmitter in a certain class of interference networks. For some classes of vector broadcast channels and X channels, I have illustrated how to optimally use distributed and moderately-delayed CSIT to yield the same sum-DoF as instantaneous and global CSIT. 

[Related Papers]
a. Namyoon Lee and Robert W. Heath Jr., “Space-Time Interference Alignment and Degrees of Freedom Regions for the MISO Broadcast Channel with Periodic CSI Feedback,” IEEE Transaction on Information Theory, vol. 60, no. 1, pp. 515-528, Jan. 2014.
b. Namyoon Lee, Ravi Tandon, and Robert W. Heath Jr., “Distributed Space-Time Interference Alignment,” Submitted to IEEE Transactions on Wireless Communications, April 2014.
c. Namyoon Lee and Robert W. Heath, “Not Too Delayed CSIT Achieves the Optimal Degrees of Freedom,” IEEE Allerton’12, Oct. 2012.
d. Namyoon Lee and Robert W. Heath, “CSI Feedback Delay and Degrees of Freedom Gain Trade-Off for the MISO Interference Channel,” IEEE Asilomar conference, Nov. 2012.

B. Interference Management for Multi-Way Communication Networks
   Due to the superposition and broadcast nature of the wireless medium, unmanaged interference results in diminishing data rates in wireless networks. With a recently developed network coding strategy, however, it was demonstrated that interference is no longer adverse in communication networks, provided that it can sagaciously be harnessed. This approach of exploiting interference has opened the possibility of better performance in the interference-limited communication regime than traditionally thought possible. For example, in wireless networks, the concept of physical layer (analog) network coding has shown that this strategy can attain higher rates over routing-based strategies under a certain network topology.
   To advance the idea of interference exploitation, I have proposed new physical-layer network coding strategies termed as signal space alignment for network coding and space-time physical-layer network coding (ST-PNC) for general multi-way communication network topologies. With theses strategies, I characterized the sum-DoF of general multi-way relay networks in terms of relevant system parameters, chiefly the number of users, the number of relays, and the number of antennas at relays. A major implication of the derived results is that efficiently harnessing both transmitted and overheard signals as side-information brings significant performance improvements to multi-way relay networks.
[Related Papers]
a. Namyoon Lee and Robert W. Heath Jr., “Space-Time Physical-Layer Network Coding,” Submitted to IEEE Journal of Selected Area on Communications, March 2014.
b. Namyoon Lee, Jong-Bu Lim, and Joohwan Chun, “Degrees of Freedom on the MIMO Y Channel : Signal Space Alignment for Network Coding,” IEEE Transaction on Information Theory, vol. 56, no. 7, pp. 3332-3342, July 2010.
c. Namyoon Lee and Joowhan Chun, “Degrees of Freedom for the MIMO Gaussian K-way Relay Channel: Successive Network Code Encoding and Decoding,” IEEE Transaction on Information Theory, vol. 60, no. 3, pp. 1814-1821, March 2014.

d. Kwang-Won Lee, Namyoon Lee, and Inkyu Lee, “Achievable Degrees of Freedom on MIMO Two-way Relay Interference Channels,” IEEE Transaction on Wireless Communications, vol. 12, no. 4, pp. 1472-1480, April. 2013.

e. Kwang-Won Lee, Namyoon Lee, and Inkyu Lee, “Achievable Degrees of Freedom on K-user Y Channels, ” IEEE Transaction on Wireless Communications, vol 11, pp. 1210 – 1219, Mar. 2012.
f. Hyun-Jong Yang, Young-Chul Kim, Namyoon Lee, and Arogyaswami Paulraj, “Achievable Sum-Rate of the Multiuser MIMO Two-Way Relay Channel in Cellular Systems: Lattice Coding-Aided Linear Precoding,” IEEE Journal of Selected Area on Communications, vol. 30, no. 8, pp. 1304-1318, Sep. 2012.

C. Interference Management for Multi-Hop Networks

   Interference management is complicated in the multi-hop networks because relay nodes between the source-destination pairs propagate the mixture of interference signals as well as desired signals on the network. This complicates the selection and design of relay strategies as it is not clear the extent to which a relay should forward, cancel, align, or otherwise manage interference. In this research direction, I have proposed interference-aware relay transmission techniques exploiting the concept of aligned interference neutralization for the multiple-input-multiple-output (MIMO) two-hop interference channels to characterize the scaling law of network sum-capacity.

[Related Papers]
a. Namyoon Lee and Chenwei Wang “Aligned Interference Neutralization and the Degrees of Freedom of the Two-User Wireless Networks with an Instantaneous Relay,” IEEE Transaction on Communications, vol. 61, no. 9, pp. 3611 – 3619, Sept. 2013.
b. Namyoon Lee and Robert W. Heath Jr., “Degrees of Freedom for the Two-Cell Two-Hop MIMO Interference Channel: Interference-Free Relay Transmission and Spectrally Efficient Relaying Protocol,” IEEE Transaction on Information Theory, vol. 59, no. 5 pp. 2882-2896, May 2013.
D. Interference Management with Limited Feedback
  Limited feedback is an essential technique for realizing advanced multi-antenna transmission techniques in multi-antenna wireless networks. With random vector quantization (RVQ) techniques, I have analyzed the impact of the limited channel state information feedback in various wireless networks.
[Related Papers]
a. Namyoon Lee and Wonjae Shin, “Adaptive Feedback Scheme on K-cell MISO Interfering Broadcast Channel with Limited Feedback,” IEEE Transaction on Wireless Communications, vol. 10, pp. 401-406, Feb. 2011

b. Junil Choi, Bruno Clerckx, Namyoon Lee, and Gil Kim, “A New Design of Polar-Cap Differential Codebook for Temporally/Spatially Correlated MISO Channels,” IEEE Transaction on Wireless Communications, vol. 11, pp. 703-711, Feb. 2012.
c. Namyoon Lee, Wonjae Shin, Robert W. Heath and Bruno Clerckx, “Interference Alignment with Limited Feedback on Two-cell Interfering MIMO-MAC,” IEEE International Symposium on Wireless Communication Systems (ISWCS), Aug. 2012. (Invited)

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