Performance of 64 kbit/s data transmission with the ARQ protocol of the DECT standard on fading channels

Abstract

This paper presents the physical and DLC layerperformances of a selective-repeat (SR) type4 hybrid ARQ protocol for the 64 kbit/s data transmission on a DECT radio interface over a Rayleigh fading or ITU indoor fading channel. Both simulation and analytical approaches are considered with perfect feedback. The real non-perfect feedback is also taken into account in the simulation approach. I IntroductionIn recent years, there has been growing interest in data transmission via wireless personal communication networks and fixed radio networks. The key technical problem is the presence of burst-error during fading periods. Forward error correction (FEC) and automatic repeat request (ARQ) are two basic error control techniques[l, ch.151. It was shown that in the Rician fading channel, FEC techniques can provide better performance than ARQ techniques, but in the Rayleigh fading channel, ARQ techniques are better[ 101. A hybrid ARQ scheme which combines FEC and ARQ offers a much better performance than either scheme alone. Two classes of hybrid ARQ schemes are categorized: type-I and type-I1 [1],[2].In this paper, we study the 64 kbit/s data transmission with the type-I hybrid ARQ data protection and the powerful selective-repeat protocol[ 11. The DECT (Digital Enhanced Cordless Telecommunication) radio interface is considered. The basic ARQ technique is specified in the LU7 standard for the DECT and ISDN inter-working configuration (Annex B in[7]). Some extensions have been made to study the performance variations. The LU7 standard has taken into account the constraints on the constant bit rate (CBR), finite buffers (i.e., fixed transmission delay) at the DLC layer and bidirectional data transmission (i.e., same protocol for the downlink and uplink). The two first constraints are studied in [8] [9].As conceming channel models, at physical layer level, we use the Rayleigh fading and ITU Indoor channels [5],[6], at DLC layer level, we use the first-order Markov model on the good or bad packet transmissions (i.e., Gilbert model) to represent the channel behavior[3] [4].The DECT radio link uses the TDD/TDMA access and GMSK modulation with 1 152 kbit/s data rate and 1.9 GHz carrier frequency. One DECT frame contains 24 time slots with the first 12 for downlink and the last 12 for uplink. The frame duration is 10 msec. The LU7 standard employs a double slot physical packet format with 960 bits, namely P80 packet format (figure 1). Two P80 packets are needed respectively for the down and up links. A-Field X-FieldGuard S-Field B-Field 2-Field -time Figurel: Structure of P80 packet format.The data field (B-field) of 8x100 bits has the frame structure represented in Fig.2 for the DLC layer service.So with 8x90=720 bits of proper information in each packet, this format can supply 72 kbitsls data rate. The bandwidth excess for a 64 kbits/s data rate service allows