Description
There are two ways to compress a discrete memoryless source by a prefix-free code: either by fixed-to-variable-length codes or by variable-to-fixed-length codes. The maximum compression is in the former case achieved by Huffman coding and in the latter case by Tunstall coding, see [1, Section 2.3].

By parsing a sequence of uniformly distributed symbols by a variable-to-fixed-length code, a sequence of non-uniformly distributed symbols can be generated. As shown in [2, Section 3.2], the variable-to-fixed-length code whose output optimally matches a given target distribution is found by geometric Huffman coding, a variant of Huffman coding.

Requirements
Interest in information theory and mathematics.

Contact
Interested? Send an email to Georg Böcherer, georg.boecherer@tum.de. Please provide some information like CV, attended lectures, grades, etc.

References
[1] J. L. Massey, Applied digital information theory I lecture notes, ETH Zurich.
[2] G. Böcherer, Capacity-achieving probabilistic shaping for noisy and noiseless channels Ph.D. dissertation, RWTH Aachen University, 2012.

In the area of research in LNT, if you already have a thesis proposal and are looking for a supervisor from LNT, you are welcome to contact me. Such a thesis broadly would fall under the following two categories.

1) External Master's/Bachelor's Thesis: You already have a proposal of thesis from one of our Industrial/Academic partners (e.g. Siemens, NSN, Intel, Fraunhofer HHI etc.) in the area of interest of LNT and you are looking for a supervisor from LNT.

2) Master's/Bachelor's Thesis at LNT: You are interested in a topic that is not on offer but is commonly studied at LNT. In this case, it is possible to make a thesis proposal in collaboration with Prof. Kramer.

Consider the problem of relay positioning for an AWGN multicast relay network. The network consists of a source, a relay and a set of destinations that want to message generated by the source. In such a scenario, it can be seen that relay positioning can result in gains in rate.

Three commonly used schemes in this scenario are: 1) Decode-and-Forward, 2) Quantize-and-Forward and 3) Amplify-and-Forward. Depending on the proximity and channel between the source and the relay each scheme perform better than the others.

Problem Statement: Prove that Decode-and-forward achieves higher rates compared to Quantize-and-forward and Amplify-and-forward relaying strategies.

Requirements: Lectures: Nachrichtentechnik. Some knowledge about cooperative strategies for relaying. Interest in math and programming.

Topic
Low-density parity-check (LDPC) codes can also be used with other fields than the binary field of size 2. An existing decoder for nonbinary (NB-LDPC) codes uses the fourier transformation for belief propagation. Apart from smaller code optimisations, a fast fourier transformation algorithm should be implemented for lower complexity and thus a faster decoding.

Requirements

• Interest in the topic
• Some experience in C and Matlab
• Basic knowledge of channel coding, especially iterative decoding algorithms would be useful

Application
Please contact Markus Stinner for your application and provide details about attended lectures and grades.

Topic
There exist different ways our institute members present research fields and topics to the public (e.g. students, other researchers). To avoid deprecated information and contact details it would be advisable to use only one common data source.
The idea is to export the data from the website (Typo3) to Powerpoint presentations and LaTeX posters. The task of the "Ingenieurspraxis" project is to implement the necessary steps in PHP to allow the usage of one common data source.

Requirements
- Interest in the topic
- Programming experience
- Experience with PHP, MySQL, LaTeX or Typo3 are very welcome

Application
Please contact Markus Stinner for your application and provide details about attended lectures and grades and about programming experience.

By using software-defined radio (SDR) equipments, the development of communication systems can be done totally in software. This allows quick prototyping of communication systems and testing them on real scenarios under real channel conditions.

In our institute, we have SDR equipments that can be used for this purpose. The aim of this work is to build a basic point-to-point wireless communication system with SDR hardware and perform channel measurements. The channel characteristics to be measured are:

• Power of the additive noise at the receiver
• Frequency error due to the oscillators
• Phase noise
• Propagation loss
• Delay (hardware delay and the propagation delay)
• Channel transfer function in time and frequency domain

• Interest in the topic
• Background in communications engineering topics
• Programming skills (in MATLAB)
• Experience with software defined radios (especially with USRP) and GNURadio is not mandatory, but is a plus

Please provide information about your attended lectures, grades and a short motivation for this topic.

More information about SDR and USRP in Wikipedia

In the work by Dierks, Kramer and Zirwas http://arxiv.org/abs/1303.5321 conditions on line-of-sight channels to ensure the feasibility of interference alignment are derived. The conditions involve choosing only the spacing between two subcarriers of an orthogonal frequency division multiplexing (OFDM) scheme. The subcarrier spacing is chosen to allow the zero-forcing of the interference.
The goal of the thesis is to determine the optimal subcarrier spacing within a certain bandwidth when optimizing the SINR (Signal to interference plus noise ratio). The results should be verified through a Matlab simualtion.

An introduction to Interference Alignment can be found in e.g. http://dx.doi.org/10.1109/TIT.2008.926344 or http://dx.doi.org/10.1109/TIT.2011.2142270.

Consider the problem of relay positioning in the context of maximizing the multicast flow from a source to a set of destinations (such a channel is also called a multicast relay channel). In the low-SNR (wideband) regime, using the decode-and-forward strategy results in the quasi-concavity of the multicast rate function as a function of relay position. This implies simple and efficient convex optimization based algorithms could be designed to solve the problem.

Problem Statement: 1) Design a simple algorithm to solve the relay positioning problem.

2) Establish the KKT conditions, prove the convergence and establish a bound on covergence.

The aim of the thesis is to design a MATLAB based Software Receiver for analyzing signals of the GNSS standard Compass (BeiDou). With the help of Rohde & Schwarz Test and Measurement equipment, signals can be recorded and saved as digital IQ samples. MATLAB’s Instrument Control Toolbox shall be used to remote control the instruments.

During the thesis work, the student should first do a literature reseach on GNSS and BeiDou standards. The acquisition, tracking and the positioning algorithms for the BeiDou standard should be studied and implemented in MATLAB. If time permits, the student should also investigate the interference between Beidou, GPS and LTE signals.

LTE has been developed to work entirely in the packet-switched domain. It was not optimised for voice calls like GSM and 3G where very specific channel configurations were defined for voice traffic. The reason for this being that LTE should use the available protocols coming from the IP world (IMS being the bridge between the IP world (IETF) and the cellular world (3GPP)). This approach, termed as Voice over LTE (VoLTE) results in the voice service (control and media planes) being delivered as data flows within the LTE data bearer. However, this flexibility comes with a price of high power consumption.

Current test results from Spirent show that a VoLTE call consumes twice as much battery life as a 2G call. Given such an issue, mobile phone operators would be reluctant to switch over to 4G technology. The intention of this Master Thesis is to analyse the defined schemes in the MAC layer in order to make a comparative study and optimise the power consumption of VoLTE.

In this regard,
- Comparison of power consumption of VoLTE as opposed to 2G and 3G.
- Disadvantage of using SVLTE as opposed to just VoLTE+LTE
- Software Architecture - Utilising the appropriate processor for a task
- Description and analysis of the MAC Layer Aspects of LTE as defined in the 3GPP Release 9 specifications. The analysis would focus on possible optimisation procedures in order to reduce power consumption during a VoLTE call.
- Investigation of defined transmission protocol schemes such as DRX, SPS, TTI bundling and RoHC for their utility in regards to power savings. This would involve studying the achievable gain in terms of battery life by varying the parameter settings, while maintaining a certain QoS.

LTE is a standard for high speed data wireless communication. Locally-defined Messages exchanged between different layers of the System Simulator (SS) contain a huge amount of information in LTE. This information is normally only displayed in a message viewer. Many messages passing between Layer 1 and MAC are sent every Transmission Time Interval (TTI) which in LTE is 1ms. Each message contains information about current User Equipment (UE) power, UE reporting (such as Channel State Indicator, CSI) and also about whether the UE remains synchronised or not. Trawling through message logs is a time-consuming process, and does not allow test equipment users to quickly focus on key problems.

A brief description of the LTE standard will be presented in the thesis. A study will be carried out on the Layer 1 (PHY), Layer 2 and Layer 3 protocol stack (possibly upper layers as well), followed by another study on the existing errors which can occur, how they propagate and how to track the root cause. Existing solutions for recognizing patterns in Uplink power from logs, determining the root cause of Out-Of-Sync of the User Equipment or solutions which quickly finds anomalies in HARQ retransmission behavior will be presented. New algorithms / solutions will be developed in this direction, with the final aim of an algorithm which will be able to intelligently search, sort and perform data fusion.

Defining different views of the same data will provide a simpler way of extracting meaningful UE state. The following areas have been identified as particularly difficult to analyse:
- Viewing current UL power, and identifying whether the UE followed Transmit Power Control (TPC) commands sent by the SS
- Downlink and Uplink HARQ transmission and retransmission behavior (not just statistics, but a representation for each retransmission whether it is adaptive, non-adaptive, and how many retransmissions were required, or if retransmission is aborted by the SS)
- HARQ retransmissions in case of MIMO, where both, or only one codeword may be ACKed or NACKed
- Carrier Aggregation in combination with HARQ retransmissions (and MIMO)
- Intelligent analysis of UE out-of-sync events: e.g. a rule-based approach to determine why the UE went OOS

R&S is currently developing an improved message analysis tool. In future the protocol-specific intelligence to display LTE-specific views could be integrated into this tool.

In 2020, mobile and wireless traffic volume is expected to increase thousand-fold over 2010 figures. Moreover, an increase in the number of wirelessly-connected devices to counts in the tens of billions will have a profound impact on society. Massive machine-type communications, forming the basis for the Internet of Things, will make the everyday life more efficient, comfortable, and safer, through a wide range of applications including traffic safety and medical services. The variety of applications and traffic types originating from or reaching mobile, WLAN, and sensor networks will be significantly larger than today and will result in more diverse requirements on services, devices, and networks.

Accordingly, there is a need to investigate network-level aspects related to the efficient deployment, operation, and optimization of the future mobile and wireless communications system. In this context, network-level solutions should be developed to address the challenges that are not sufficiently addressed by currently available systems.

Within the framework of this thesis, the student will first survey and familiarize with the state-of-the-art signaling schemes, e.g., in the current 4G mobile networks. Then, the student should investigate network-level concepts for a more efficient handling of signaling, which can significantly increase due to, e.g., massive machine-type communications. Furthermore, signaling schemes should be adapted to new integrated communications types, such as network-controlled direct device-to-device communications. Performance evaluation of the different schemes is to be carried out using a network-level simulator.

At 1CM9 we are using a MATLAB-based testbed that behaves like an LTE / LTE-Advanced UE (user equipment) to verify latest functionality in the R&S CMW500 Mobile Communications Tester platform. This MATLAB UE platform shall be extended to support the Transmission Mode 9 (TM9) of LTE-Advanced, which comprises a beamformed downlink transmission with up to eight MIMO layers. The proposed Master Thesis should cover the following tasks:

* Description and analysis of the physical layer aspects of LTE-A TM9 as specified in 3GPP Release 10 specifications. The analysis should emphasize on the interaction between the pre-defined CSI reporting codebooks and the resulting transmission patterns and elaborate how the data transmission in TM9 is optimized in comparison to other transmission modes (e.g. TM4 (closed-loop spatial multiplexing) and TM8 (dual-layer beamforming)).

* Extension of the existing UE downlink receiver architecture to decode DCI format 2C and the associated PDSCH (physical downlink shared channel) communication using UE-specific reference signals with up to two spatial multiplexing layers (ports 7 and/or 8).

* Extension of the CSI (channel state information) reporting mechanisms on the UE side to support the extended formats of TM9 (i.e. reports based on up to eight layers of CSI-RS, new reporting types and precoding matrices for aperiodic and periodic reports).

* Test of basic signalling functionality by performing a call setup between the CMW500 and the MATLAB UE environment using TM9. The implementation has to first cover 1x1, 1x2 and 2x2 MIMO and should later be extended for 4x2 and 8x2 MIMO configurations.

Background:
The OFDMA-based access scheme in the downlink of LTE provides amble flexibility for dynamic radio resource management. In conjunction with the channel state information (CSI) reporting schemes standardized for LTE / LTE-A it offers potential to exploit the variations of the fading channel over time and frequency to achieve significant scheduling gains, that is gains over CSI-ignorant scheduling schemes. Together with Turbo codes operating in close proximity to the information-theoretic capacity of the individual link, potential for performance improvements given a certain SINR distribution appears to be largely exhausted.

Focus in radio resource management has hence moved towards reduction of interference power among different cells of the mobile communication network by means of coordination or cooperation, mostly to improve the channel conditions for users located at the boundaries between different radio cells. Here, different degrees of coordination / cooperation are being considered, ranging from a coordination of the scheduling decisions of individual cells possibly in combination with beam forming over dynamic cell selection, a similar technique with the additional feature that users can be assigned resources dynamically in different cells, to so-called joint-transmission cooperative multi-point, where the antenna arrays of the different base stations are essentially regarded as one large MIMO antenna array and cooperative scheduling across several cells is based on the principles of multi-user MIMO scheduling. The latter only works effectively with detailed CSI at the transmitter side, which induces major signalling overhead in the uplink. In this work, we hence want to focus on the less demanding approach of coordinated scheduling.

Tasks:
Building upon Nomor's comprehensive LTE/LTE-A system-level simulator, which has—besides some built-in scheduling algorithms—an API to attach independently developed scheduling algorithms the student shall
- implement his/her own uncoordinated single-cell scheduling algorithm to familiarize him-/herself with the API and the fundamentals of OFDMA-based radio resource management and to have a suitable reference,
- study the literature on existing proposals for coordinated scheduling,
- develop, implement and analyse algorithms for coordinated multi-cell scheduling, first without beam forming and ideally (if time permits and if deemed promising) in combination with beam forming.

By using software-defined radio (SDR) equipments, the development of communication systems can be done totally in software. This allows quick prototyping of communication systems and testing them on real scenarios under real channel conditions.

In our institute, we have SDR equipments that can be used for this purpose. The aim of this work is to build a communication systems to test and evaluate the performance of different relaying techniques like Decode-and-Forward, Amplify-and-Forward and Quantize-and-Forward. The tasks of the student can be listed as follows:

• Literature review on the relaying techniques and their theoretical performance evaluation,
• Implementation of the techniques with SDR,
• Performance evaluation of the techniques according to different criteria (transmit power, relay location, resource allocation parameters, etc.),
• Performance evaluation of the systems with multiple relays (optional).

• Interest in the topic,
• Background in communications engineering topics,
• Programming skills (in MATLAB),
• Experience with software defined radios (especially with USRP) and GNURadio is not mandatory, but is a plus.

Please provide information about your attended lectures, grades and a short motivation for this topic.

• More information about SDR and USRP in Wikipedia
• Kramer, G., Marić, I., & Yates, R. D. (2006). Cooperative communications. Foundations and Trends in Networking, 1(3), 271-425.