Jerome Brouet

Compression of associated signaling for adaptive multi-carrier systems

Link adaptation technology has been introduced in new generation transmission systems, such as 3G and 4G, optimizing both their throughput and their power consumption. Adaptation of the radio configuration requires information about the radio link quality. The information must be exchanged between the access point and the mobile terminal, leading to an associated signaling load, whose amount may decrease the system transmission efficiency. A mechanism for reducing the amount of signaling information has to be designed to increase the overall system capacity (more users, more available bandwidth). The paper addresses multi-carrier systems whose link adaptation is carried out by means of bit loading algorithms. However, the associated signaling load increases quickly with the number of sub-carriers, modulation schemes and users. These bit loading vectors are considered a-priori known at the receiver, and almost no literature concerning transmission of such information is available. In realistic transmission systems, correlation exists in time due to Doppler effects, and in frequency due to multipath delay spread. We intend to exploit this twofold redundancy to decrease signaling information load. An adaptive lossless compression system for an optimized compression performance and complexity is proposed, giving much higher compression ratio than the existing LZW bit loading algorithm (Lestable, T. and Battelli, M., 2002).

Robust VLC sequence decoding exploiting additional video stream properties with reduced complexity

Joint source-channel decoding of variable length codes (VLC) for image and video streaming transmission over unreliable links, such as wireless networks, is a subject of increasing interest. Much more residual source redundancy can be exploited when both types of correlation: (i) the correlation between bits inside a VLC codeword as well as; (ii) the correlation between VLC codewords of a VLC sequence unit (e.g. corresponding to one image block), are taken into account. The paper (Hang Nguyen et al, IEEE Int. Conf. on Acoustics, Speech, and Sigpro., 2004) proposes an optimum maximum likelihood (ML) decoder of VLC sequences which can exploit these two kinds of correlation and outperforms the existing VLC decoders. This paper proposes a reduced complexity version of this optimal VLC decoder. Simulation results show that the complexity is reduced by 5 in terms of number of possible candidates, while the performance is only slightly sub-optimal compared with the optimal version of the Hang Nguyen paper.

Efficient evaluation of voice quality in GERAN (GSM EDGE Radio Access Network)

The transport of multimedia application is now a key feature of the future radio access networks. The evolution of GSM networks is also able in principle to take benefit from end-to-end transfer of such applications. However, careful attention has to be taken regarding the quality perceived by the end user. Indeed, for voice services, mobile subscribers are familiar with a given quality. The introduction of IP services should not decrease this quality. Besides, the introduction of such feature on the radio links should also enable the operators to increase their network capacity. In this context, this paper analyses the perceived voice quality when voice frames are transported on existing packet radio bearers of GSM/EDGE Radio Access Networks. In this situation, the benefit for the operator should be maximal. The quality is evaluated with an objective method that relies on comparison of reference speech sequence with the same sequence that is passed through GERAN radio links. This methodology of evaluation if by far more consistent than simply considering radio link level performance like the bit error rate.

Performance of a distributed coverage SFH-TDMA system with mobility management in a high density traffic network

Low probability of blocking (Pb) at call set-up and very low probability of forced call termination (Pf), are important design criteria for micro and pico-cell networks deployed for very high traffic density areas like dense urban and indoors. In conventional cellular networks with fixed channel allocation (FCA), fine tuning of radio resource management (RRM) algorithms like channel selection (CS), channel change (CC) and handover (HO) is thus a difficult task. The difficulty is further increased because a higher number of handovers per call has to be handled. A new network architecture based on the concept of distributed radio coverage has been found to manage mobility and interference in high density traffic areas for TDMA systems like GSM/DCS, IS-54/IS-136. This paper focuses on RRM algorithms for such an approach whereby the coverage of a single cell is realised with synchronised relays using the same broadcast channel. The conventional HO is replaced by progressive channel activation on predicted best server relays. Five different strategies for channel selection/activation, ranging from channel activation on one best server antenna to simultaneous channel activation on all the antennas of a cell, have been evaluated. A mix of information of subscriber mobility and the existing traffic load on the cell is shown to have a determining influence on the channel selection/activation strategies offering maximum traffic throughput and minimum Pf.

Teletraffic analysis of enhanced circuit switched data (ECSD) on GSM for mobile multimedia services

The Global System for Mobile Communications (GSM) has been a great success in providing both voice and low speed data services. The current evolution of GSM towards the third generation mobile communications system is attributed to its remarkable growth and also to the increasing demand for mobile data. The enhanced circuit switched data on GSM (ECSD) is one of the major evolutionary steps to serve real time high speed data services such as real time video and or file transfer. The ECSD enhances the bandwidth by combining several time slots and by utilizing efficient modulation and coding schemes. In this paper we present a Markov analysis of ECSD and compare its performance with the existing high speed circuit switched data on GSM (HSCSD), which also uses multi-slot allocation but with a conventional GSM physical air-interface. In this analysis we also consider the transmission errors on the radio interface. The results of the comparative analysis are presented in terms of grade of service, average throughput and average message transfer delay taking into account eventual transmission errors on the radio link.

Deployment of multi-layer TDMA cellular network with distributed coverage for traffic capacity enhancement

In second generation TDMA cellular systems, traffic increase is achieved via cell size reduction. But, to handle moving mobile stations (MS) and ensure coverage on the whole served area, a 2-layer network has to be deployed and radio resource management techniques such as directed retry (DR) are implemented for spectrum efficiency. Optimally, fast (respectively, slow) moving MS should be served by the macrocell (respectively microcell) layer. So, in such network organization, traffic performance is sensitive to both coverage quality and accuracy of estimation of MS speed. Conventional microcell layer deployment suffers from coverage holes and uncertainty of speed estimate (making it impossible to exploit the full capacity of such networks). This paper proposes to replace the usual layer of microcells by a distributed coverage. Strategies for serving base transceiver station (BTS) selection and channel allocation dependent on MS position over the service area, are implemented. Both the communication quality and the accuracy of estimation of MS speed are improved. This makes DR more efficient and enhances the overall traffic performance.

Low complexity algorithm for the decoding of convolutional codes of any rate

It is well known that convolutional codes can be optimally decoded by using the Viterbi algorithm (VA). A decoding technique where the VA is applied to identify the error vector rather than the information message is proposed. We previously focused on convolutional coders of rate 1/2 . The method to codes of any rate is generalized and shows that, with the proposed type of decoding, the exhaustive computation of a vast majority of state to state iterations is unnecessary. Hence, performance close to optimum is achievable with a significant reduction of complexity. The higher the SNR, the greater the improvement for reduction in complexity. For instance, for SNR greater than 3 dB, a five fold reduction in complexity for the computation of ACS (add compare select) is achieved.

Robust and adaptive transmission of compressed video streams over EGPRS

Today, multimedia transmission over wireless networks encounters several problems and the result is a poor video quality perceived by the end-user. The paper investigates the feasibility of video streaming transmission over EGPRS mobile networks. Then, a simple system of variable-to-fixed length code is proposed to get a more robust compressed data. Hence, more robust data can be transmitted with less error protected EGPRS modulation and coding schemes which allow higher data rates.

Impact of adaptive modulation on MC-CDMA receiver in beyond 3G systems

The study presented in this paper underlines the capacity increase resulting from the joint use of multicarrier (MC) adaptive modulation techniques and MC-CDMA receiver in the context of beyond 3G systems. The performance enhancement due to such near optimal rate and power adaptation decreases with diversity order. Moreover, results obtained through two different kinds of wireless channels (ETSI BRAN A and C) highlight convergence phenomena, independent of initial channel diversity order. Finally, complete single user detection (SUD) techniques are compared in tit is context of adaptive modulation.

Low complexity algorithm for soft decoding of convolutional codes

It is well known that convolutional codes can be optimally decoded by the Viterbi algorithm (VA). We propose a soft decoding technique where the VA is applied to identify the se error vector rather than the information message. In this paper, we show that, with this type of decoding, the exhaustive computation of a vast majority of state to state iterations is unnecessary. Hence, performance close to optimum is achievable with a reduction of complexity. The gain in complexity of the proposed scheme is all the more important as the SINR is high. For instance, for SNR greater than 3 dB. more than 80% of id-rations and more than 84% of computations for ACS (add compare select) can be avoided.