Adding Integrity Verification Capabilities to the LDPC-Staircase Erasure Correction Codes

File distribution is becoming a key technology, in particular in large scale content broadcasting systems like DVB-H/SH. They largely rely on Application Level FEC codes (AL-FEC) in order to recover from transmission erasures. We believe that sooner or later, content integrity and source authentication security services will be required in these systems. In order to save the client terminal resources, which can be a handheld autonomous device, we have designed a hybrid system that merges the AL-FEC decoding and content integrity/source authentication services. More precisely our system can detect a random object corruption triggered by a deliberate attack with a probability close to 100% almost for free in terms of computation overhead

Improving Group Integrity of Tags in RFID Systems

Checking the integrity of groups containing radio frequency identification (RFID) tagged objects or recovering the tag identifiers of missing objects is important in many activities. Several autonomous checking methods have been proposed for increasing the capability of recovering missing tag identifiers without external systems. This has been achieved by treating a group of tag identifiers (IDs) as packet symbols encoded and decoded in a way similar to that in binary erasure channels (BECs). Redundant data are required to be written into the limited memory space of RFID tags in order to enable the decoding process. In this thesis, the group integrity of passive tags in RFID systems is specifically targeted, with novel mechanisms being proposed to improve upon the current state of the art. Due to the sparseness property of low density parity check (LDPC) codes and the mitigation of the progressive edge-growth (PEG) method for short cycles, the research is begun with the use of the PEG method in RFID systems to construct the parity check matrix of LDPC codes in order to increase the recovery capabilities with reduced memory consumption. It is shown that the PEG-based method achieves significant recovery enhancements compared to other methods with the same or less memory overheads. The decoding complexity of the PEG-based LDPC codes is optimised using an improved hybrid iterative/Gaussian decoding algorithm which includes an early stopping criterion. The relative complexities of the improved algorithm are extensively analysed and evaluated, both in terms of decoding time and the number of operations required. It is demonstrated that the improved algorithm considerably reduces the operational complexity and thus the time of the full Gaussian decoding algorithm for small to medium amounts of missing tags. The joint use of the two decoding components is also adapted in order to avoid the iterative decoding when the missing amount is larger than a threshold. The optimum value of the threshold value is investigated through empirical analysis. It is shown that the adaptive algorithm is very efficient in decreasing the average decoding time of the improved algorithm for large amounts of missing tags where the iterative decoding fails to recover any missing tag. The recovery performances of various short-length irregular PEG-based LDPC codes constructed with different variable degree sequences are analysed and evaluated. It is demonstrated that the irregular codes exhibit significant recovery enhancements compared to the regular ones in the region where the iterative decoding is successful. However, their performances are degraded in the region where the iterative decoding can recover some missing tags. Finally, a novel protocol called the Redundant Information Collection (RIC) protocol is designed to filter and collect redundant tag information. It is based on a Bloom filter (BF) that efficiently filters the redundant tag information at the tag’s side, thereby considerably decreasing the communication cost and consequently, the collection time. It is shown that the novel protocol outperforms existing possible solutions by saving from 37% to 84% of the collection time, which is nearly four times the lower bound. This characteristic makes the RIC protocol a promising candidate for collecting redundant tag information in the group integrity of tags in RFID systems and other similar ones

Adding Integrity Verification Capabilities to the LDPC-Staircase Erasure Correction Codes

With the advent of broadcast/multicast systems, like DVB-H, large scale content broadcasting is becoming a key technology. This type of data distribution scheme largely relies on the use of Application Level Forward Error Correction codes (AL-FEC), not only to recover from erasures but also to improve the content broadcasting scheme itself (e.g. FLUTE/ALC). This work focuses on the LDPC-staircase large block FEC codes that are well suited to these services, and for which an open source codec is available. We believe that sooner or later these broadcasting systems will require security services. Therefore, the current work focuses on the content integrity service, which is one of the key security building blocks. More and more often (and in particular in the context of DVB-H), the client terminal will be a handheld autonomous device with limited battery capacity. In order to save the client terminal resources, we have focused on a hybrid system that merges the FEC decoding and content integrity verification services. This hybrid system takes advantage of a corruption propagation phenomenon during the FEC decoding process in order to perform integrity verification. Thanks to this approach, we have been able to design a high performance hybrid codec that keeps the same erasure recovery capabilities of the LDPC-staircase codes while providing a Content Integrity Verification service almost for free. More precisely this system can detect an object corruption triggered by deliberate attacks or by transmission errors (not detected by lower layer protocols) with a very high probability (close to 100%) with a processing overhead that is only a minimal fraction (around 6.2%) of the overhead of a hash calculation over the whole object, which is the usual way to address the problem. Finally, we explain how to extend this system in order to provide a 100% detection guarantee, or how this system can help to mitigate a Denial of Service attack

Adding Integrity Verification Capabilities to the LDPC-Staircase Erasure Correction Codes

apport de recherch

Performance analysis of 4G wireless networks using system level simulator

Doutoramento em Engenharia ElectrotécnicaIn the last decade, mobile wireless communications have witnessed an explosive growth in the user’s penetration rate and their widespread deployment around the globe. In particular, a research topic of particular relevance in telecommunications nowadays is related to the design and implementation of mobile communication systems of 4th generation (4G). 4G networks will be characterized by the support of multiple radio access technologies in a core network fully compliant with the Internet Protocol (all IP paradigms). Such networks will sustain the stringent quality of service (QoS) requirements and the expected high data rates from the type of multimedia applications (i.e. YouTube and Skype) to be available in the near future. Therefore, 4G wireless communications system will be of paramount importance on the development of the information society in the near future. As 4G wireless services will continue to increase, this will put more and more pressure on the spectrum availability. There is a worldwide recognition that methods of spectrum managements have reached their limit and are no longer optimal, therefore new paradigms must be sought. Studies show that most of the assigned spectrum is under-utilized, thus the problem in most cases is inefficient spectrum management rather spectrum shortage. There are currently trends towards a more liberalized approach of spectrum management, which are tightly linked to what is commonly termed as Cognitive Radio (CR). Furthermore, conventional deployment of 4G wireless systems (one BS in cell and mobile deploy around it) are known to have problems in providing fairness (users closer to the BS are more benefited relatively to the cell edge users) and in covering some zones affected by shadowing, therefore the use of relays has been proposed as a solution. To evaluate and analyse the performances of 4G wireless systems software tools are normally used. Software tools have become more and more mature in recent years and their need to provide a high level evaluation of proposed algorithms and protocols is now more important. The system level simulation (SLS) tools provide a fundamental and flexible way to test all the envisioned algorithms and protocols under realistic conditions, without the need to deal with the problems of live networks or reduced scope prototypes. Furthermore, the tools allow network designers a rapid collection of a wide range of performance metrics that are useful for the analysis and optimization of different algorithms. This dissertation proposes the design and implementation of conventional system level simulator (SLS), which afterwards enhances for the 4G wireless technologies namely cognitive Radios (IEEE802.22) and Relays (IEEE802.16j). SLS is then used for the analysis of proposed algorithms and protocols.FC