Influence of Retransmissions on the Estimating Number of Users Associate in a WLAN Using Error Pron-Channel Haider M. AlSabbagh 1 and Ali Amin 2 Department of Electrical Engineering, College of Engineering, Basra University Basra, Iraq 1 haidermaw@gmail.com , 2 aliaiq76@yahoo.com Abstract—Recently, the IEEE 802.11 WLANs are experiencing a vast popularity and widespread deployment particularly with the rapid development in wireless communication technologies. Designing WLANs with traditional steps may allow a specific number of users to utilize from facilities of the networks. The transmission channel condition and number of sharing users are crucial information to be known for the adaptive networks towards achieving better performance. Although numerous of considerable studies investigated estimating number of sharing users in a WLAN utilizes an error-prone channel, influence limited number of retransmissions and type of the accessing transmission channel mechanism on the number of sharing stations are still required more investigation. Therefore, this paper is conducted to analyze these effects. Analytical expressions are presented for studying these effects. The achieved results show that the limited number of retransmissions has a substantial impact on the estimation number of sharing stations using an error-prone channel while type of the access mechanism has ignorable influence on the estimation process. Keywords-IEEE 802.11 DCF; WLAN; MAC protocol; Error- prone channel; performance evaluation. I. INTRODUCTION In the recent years wireless local area networks (WLANs) have gained popularity due to providing relatively high- bandwidth operation for interconnecting mobile devices and providing access to the internet with its relatively low coast establishment requirements [1]. WLANs operating at the unlicensed ISM frequency bands is one of the available solutions to satisfy the most demands for the next generation communications (subscribe accessible at any time and at anywhere) [2]. Also, it able to comply with fastest growing segments in the communications industry. WLANs have been getting more attractiveness, particularly with producing the new equipments and establishing new standards such as IEEE 802.11n and VoWi-Fi and infrastructure for traditional Wi-Fi expands [2, 3]. The physical media in the WLANs is shared between all stations and has limited connection range compared with its wired counterpart. The MAC protocol defined two functions, namely distributed coordination function (DCF) and the optional point coordination function (PCF). DCF defines two mechanisms to access transmission medium: the two-way (basic) access scheme, which is the default scheme and the request to send/clear to send (RTS/CTS) scheme, also known as four-way handshaking scheme [3, 4]. DCF has superior attractiveness over PCF in many aspects [5]; therefore this paper is conducted to investigate number of users in a WLAN utilizing DCF. In dynamic and media sharing wireless environment, the capacity enhancements at individual channel may not necessarily benefit, and sometimes even degrade the system performance with multiple users. As we have pointed out in the previous work [6] that to get closer look to the real situation in the WLANs influence of channel condition and the type of mechanism should be taken into the consideration. It has been shown that in multi-user network, throughput can be increased; hence amount of packet delay substantially decreased if a partial knowledge of the channel condition and number of sharing stations are known. The adaptive stations might utilize such information to change the utilized accessing mechanism and some other tunable parameters such as minimum contention window size, data rate, retry limit and length of packets accordingly to the MAC layer as controllable variables. The work in [6] had continued the series of derivations towards providing a completed analytical model. The model has taken into account influence the number of retransmissions, the error level in the utilizing transmission channel, type of the transmission channel mechanism, and the size of the network (number of sharing stations with an access point). While Bianchi and Tinnirllo in Ref. [7] have continued the efforts to estimate number of sharing users utilizing Bianchi's idealistic model, presented in Ref. [8], which based on the assumption that the collision is the only error, packet retransmits are unlimited and a packet is being transmitted continuously until its successful reception. In this paper, the model in Ref. [6] and procedure in Ref. [7] are adopted to formulate the related relations to estimate number of sharing users. Influences of limited number of retransmissions, type of the access channel mechanism and error due to the transmitting channel are considered. The achieved results show that in the error-prone channel the designed maximum number of retransmissions and amount of error in the channel play the key role to estimate the available number of sharing stations, while type of the utilized mechanism has ignorable information on the estimating 978-1-4244-3693-4/09/$25.00 ©2009 IEEE Authorized licensed use limited to: Iraq Virtual Science Library. 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