Single Input Multiple Output techniques for

Currently, there are three broadband :LUHOHVVV/RFDOO$UHD1HWZRUNV (WLAN) standards harmonised at the physical layer (based on OFDM) that operate in the 5 GHz band, i.e. ETSI BRAN HL/2 in Europe, IEEE 802.11a in the USA and ARIB MMAC HiSWAN in Japan. This paper focuses on the use of adaptive antennas for HL/2 [ETSI00]. The system shall be adapted to work in different propagation and interference scenarios, thus the use of adaptive antennas is motivated. In general, the array techniques with multiple inputs and/or outputs can be deployed for range extension, delay spread or interference suppression and capacity increase. In the HL/2 context, the interferences seem to be the most pernicious effect. Then, with the motivation to be standard compliant the SIMO approach is studied. The analysed techniques in this paper can be classified into diversity combining (MRC) or spatial adaptation (SMI [Vook98] and MDIR [Lagunas00]). In order to study the application of these techniques, a realistic modelling of the HL/2 frame structure has been performed. A frame is transmitted each 2 ms in a dynamic TDMA/TDD structure. A variety of modulations (from BPSK to 64QAM) and code rates are available which provide seven modes. Their transmission rates at physical layer range from 6 to 54 Mbit/s. With a sampling frequency of 20 MHz, the duration of the OFDM symbol is 4 µs, which means 80 samples after the analogue to digital conversion, 64 of useful data and 16 of the cyclic prefix (CP). This CP shall be sufficient to avoid ,QWHU6\PERO ,QWHUIHUHQFH (ISI) and ,QWHU&DUULHU ,QWHUIHUHQFH (ICI) in most situations, but not for channel model 'E' among those specified by BRAN in [Medbo98]. 52 subcarriers are available in a bandwidth of 20 MHz, 48 of which are useful data carriers and the other 4 are pilots. The rest of samples to complete the 64 to perform the IFFT/FFT operations at the transmitter and at the receiver are padding zeros. The data transmission is packet oriented. A burst is a set of packets for a certain user, preceded by a preamble. This preamble serves for synchronisation as well as for automatic gain control and channel estimation and is the same for all users but depends on the type of burst. This paper is organised as follows. Section II specifies the signal model and notation for the multicarrier SIMO system. Section III addresses the important problem of channel estimation and studies the suitability …