Abstract
In large wireless installations based on WLAN systems, mechanisms governing their operation other than just those related to the radio coverage may play a crucial role in the customer experienced quality of service (EoS). In particular, two factors have been identified as having a particular impact on the final efficiency of the distributed WLAN network. The first one is the IEEE 802.11x protocol overhead (assisted with the choice of the preamble length) which is largely dependent on the kind of WLAN standard used – ‘b/g’, ‘a’ or ‘n’. The other factor is the MAC protocol scheme, the CSMA/CA, developed for the IEEE 802.11x family, identical for all its sub-standards. A simple formula has been developed that accounts for both these aspects and provides an easy-to-implement method allowing deployment of the minimum number of access points as a function of the expected number of users, assuring a guaranteed effective throughput per user at optimal utilization of the total available capacity. DOI: http://dx.doi.org/10.5755/j01.eee.19.9.5658
Highlights
The technology addressed in the paper grounded on the IEEE 802.11x family of standards started off as a wireless extension to home local area networks; its usability has quickly been appreciated in other applications
Unlike cellular technologies that involve intensive research prior to deployment, the development of WLAN-based wide coverage networks has followed an trial-and-error path with very little theory on effective planning of such networks. Keeping pace with such a rampant growth of application space is an uneasy task, some efforts have been made on developing methods for optimal planning; either regarding the determination of optimal locations for a group of cooperating access points or evaluating their number based on the adaptive channel selection or the radio coverage (e.g. [1]–[7])
The simple formula allows one to quickly estimate the number of access points (APs) of a certain kind, specifying on the input the total expected number of users NUS, the physical data rate rate at the physical layer (RPHY) offered by the APs and the throughput RUS one wishes to guarantee the end user, above MAC layer
Summary
The technology addressed in the paper grounded on the IEEE 802.11x family of standards started off as a wireless extension to home local area networks; its usability has quickly been appreciated in other applications. Equations (2) and (3) define RMAC1 for WLAN ‘a/g’ and ‘n’, respectively, where TSYM – the OFDM symbol duration, L – the user data length, LACK – the acknowledgement frame length, NDBPS – the number of usable bits per OFDM symbol, NSS – number of antennas in the MIMO scheme (see [9]–[12] for more information) This feature, in turn, is attributed to the fact that the preamble and the PLCP header transmission as well as the multiple access procedures are only performed for a single spatial data stream – all the other streams are free from this overhead and contribute to the steep increase rate for even small or moderate packets: RMAC1.
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