Generalized Alamouti Codes for Trading Quality of Service against Data Rate in MIMO UMTS
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Generalized Alamouti Codes for Trading Quality of Service against Data Rate in MIMO UMTS ¨ Christoph F. Mecklenbrauker Forschungszentrum Telekommunikation Wien (ftw), Donau-City Straße 1, 1220 Vienna, Austria Email: [email protected]
Markus Rupp Institut f¨ur Nachrichtentechnik und Hochfrequenztechnik, Technische Universit¨at Wien, Gusshausstraße 25-29, 1040 Vienna, Austria Email: [email protected] Received 17 December 2002; Revised 26 August 2003 New space-time block coding schemes for multiple transmit and receive antennas are proposed. First, the well-known Alamouti scheme is extended to NT = 2m transmit antennas achieving high transmit diversity. Many receiver details are worked out for four and eight transmit antennas. Further, solutions for arbitrary, even numbers (NT = 2k) of transmit antennas are presented achieving decoding advantages due to orthogonalization properties while preserving high diversity. In a final step, such extended Alamouti and BLAST schemes are combined, offering a continuous trade-off between quality of service (QoS) and data rate. Due to the simplicity of the coding schemes, they are very well suited to operate under UMTS with only very moderate modifications in the existing standard. The number of supported antennas at transmitter alone is a sufficient knowledge to select the most appropriate scheme. While the proposed schemes are motivated by utilization in UMTS, they are not restricted to this standard. Keywords and phrases: mobile communications, space-time block codes, spatial multiplexing.
1.
INTRODUCTION
One of the salient features of UMTS is the provisioning of moderately high data rates for packet switched data services. In order to maximize the number of satisfied users, an efficient resource assignment to the subscribers is desired allowing flexible sharing of the radio resources. Such schemes must address the extreme variations of the link quality. Standardization of UMTS is progressing steadily, and various schemes for transmit diversity [1] and high-speed downlink packet access (HSDPA) with multiple transmit and receive antennas (MIMO) schemes [2] are currently under debate within the Third Generation Partnership Project (http://www.3gpp.org/). Recently, much attention has been paid to wireless MIMO systems, (cf. [3, 4, 5]). In [6, 7], it was shown that the wireless MIMO channel potentially has a much higher capacity than was anticipated previously. In [8, 9, 10], spacetime coding (STC) schemes were proposed that efficiently utilize such channels. Alamouti [11] introduced a very simple scheme allowing transmissions from two antennas with the same data rate as on a single antenna but increasing the diversity at the receiver from one to two in a flat-fading channel. While the scheme works for BPSK even with four
and eight antennas, it was proven that for QPSK, only the two-transmit-antenna scheme offers the full diversity gain [8, 12]. In order to evaluate the (single-) symbol error probability for a random channel H with NT statistically independent transmission paths with zero-mea
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