Packet level acknowledgement and Go-Back-N protocol performance in infrared wireless LANs

V. Vitsas, A. Boucouvalas
2003 International Journal of Communication Systems  
Infrared wireless LANs may employ repetition rate (RR) coding to increase the symbol capture probability at the receiver. This paper examines the effectiveness of RR coding to utilization for infrared LANs using the physical and link layer parameter values proposed in the Advanced Infrared (AIr) protocol standard, which is developed by the Infrared Data Association (IrDA). Infrared LANs employ a Go-Back-N (GBN) automatic repeat request (ARQ) retransmission scheme at the Link Control (LC) layer
more » ... o ensure reliable information transfer. To efficiently implement RR coding, the receiver may return after every DATA packet a suggestion for the suitable RR value to be used by the transmitter and implement a Stop-and-Wait (SW) ARQ scheme at the medium access control (MAC) layer. The effectiveness of employing this optional SW ARQ scheme at the MAC layer is discussed. Analytical models for the ARQ retransmission schemes are developed and employed to compare protocol utilization for different link parameter values such as window size, packet length and LC time out periods. This analysis identifies the ARQ protocol that maximizes performance for the specific link quality and the implemented link layer parameters. The effectiveness of the proposed RR coding to LAN utilization for different ARQ scheme implementation is finally explored. This analysis identifies the link quality level at which RR should be adjusted for maximum performance. It is concluded that if the packet error rate is higher than 0.1-0.4 (depending on the implemented ARQ protocol), the receiver should advise the transmitter to double the implemented RR for maximum performance. These error rate values are high and can be effectively estimated by the transmitter based on packet retransmissions. Thus, the usefulness of the receiver indicating to the transmitter to adjust RR is questionable, as the transmitter can effectively implement the suitable RR value based on packet retransmissions. candidate for wireless LANs [1] [2] [3] [4] . Infrared systems are confined to the room of operation, have very high bandwidth, high data rates, small physical size, low cost, low power and utilize an unregulated spectrum [1, 5] . However, IR link signal-to-noise ratio (SNR) is affected by sunlight, fluorescent light, diffuse propagation paths and physical obstacles obstructing the line of sight [5] . IR links should be of high dynamic range and capable of operating under variable SNR. As IR wireless links may suffer from transmission errors, a reliable retransmission scheme is required to ensure correct reception of the transmitted information. Infrared Data Association (IrDA) was formed in 1993 aiming to develop standards for indoor connectivity using the infrared spectrum. IrDA developed the IrDA 1.x protocol standard [1, 6] for low cost, short range, narrow beam, point-to-point and half-duplex links [7] . The success of IrDA 1.x standard can be measured by the number of mobile devices on market today, ranging from laptops to mobile phones, embedding a low-cost infrared port for wireless communications. IrDA has proposed the Advanced Infrared (AIr) protocol standard for wireless LANs [2, 8] . IrLAP, the IrDA 1.x data link layer [9], was split into three sub-layers, the AIr medium access control (AIr-MAC) [10], the AIr link manager (AIr-LM) and the AIr link control (AIr-LC) [11] sub-layers. A new physical layer, AIr PHY [8, 12] , is proposed employing wide angle infrared ports capable of operating at angles up to AE608: AIr PHY employs a four-slot pulse position modulation with variable repetition encoding (4PPM/VR) format. The base data rate is 4 Mbps: The transmitter utilizes repetition rate (RR) coding for operation at a low SNR [4, 13] . Every transmitted symbol is repeated RR times in order to increase the symbol capture probability at the receiver. RR coding results in a improved link quality at the expense of lower link data rate. The receiver monitors channel quality and advises the transmitter of the suitable RR to be used [10] . RR coding is a way of adapting the link rate to channel conditions. AIr protocol also uses the request-to-send/clear-to-send (RTS/CTS) packet exchange to reserve the infrared medium and to cope with hidden stations [14] . A successful reservation is always terminated by using the end-of-burst/end-of-burst confirm (EOB/EOBC) packet exchange to inform all stations that the current reservation is over and to synchronize all competing stations in contending for medium access. This work considers AIr MAC and LC layer implementation by identifying the link layer issues and parameters that maximize performance, such as the reliable retransmission scheme, suitable RR value, the transmission control passing mechanism and window and frame size. AIr protocol proposes a Go-Back-N (GBN) automatic repeat request (ARQ) retransmission scheme at the LC layer [11, 15] . To efficiently implement RR coding under varying SNR, the receiver may return after every DATA packet a suggestion for the suitable RR value to be used for the specific SNR. As the packet carrying this suggestion also acknowledges the received DATA packet, an optional Stop-and-Wait (SW) ARQ scheme at the medium access control (MAC) layer is implemented [10, 15] . The effectiveness of using the optional SW ARQ scheme at the MAC layer when the GBN ARQ scheme is implemented at the LC layer is studied in References [15, 16] for LANs with one transmitting station. Presented results are enhanced for the same ARQ schemes (referred to as PLACK and NoPLACK protocols) in References [17, 18] . This work offers a complete analysis of AIr's ARQ schemes by considering (in addition to PLACK and NoPLACK protocols) variations of the proposed ARQ schemes (referred to as PLACK-M and NoPLACK-ACK protocols) that result in better performance. This work also considers LANs with many transmitting stations. The GBN ARQ scheme passes transmission control by setting the Poll/Final (P/F) bit in the control field of a transmitted packet. AIr LC specification [11] defines that the P/F bit may be set in a DATA or in an LC Receive Ready acknowledgement (ACK) packet. This paper compares
doi:10.1002/dac.575 fatcat:u3p4d7vt6rf3fgefru2bkfxzhm