Abstract
We present a hybrid soft detector that has a good performance/complexity trade-off for a multiple-input multiple-output (MIMO) wireless communication system with known channel information. The new soft detector combines the merits of a simple unstructured least-squares (LS)-based soft detector and a list sphere decoder (LSD)-based soft detector for data bit detection. The former is computationally much more efficient than the latter at the cost of poorer performance. The poor performance of the former occurs mainly when the channel matrix is ill-conditioned. Whenever this happens, we use the LSD-based soft detector in the hybrid soft detector; otherwise, we use the LS-based one. Moreover, we provide a tight radius for a sphere decoder, a hard detector, via using the output of an LS-based hard detector. These two hard detectors are needed to determine if LS or LSD should be used in the hybrid soft detector. As an application example, we consider doubling the maximum data rate of the IEEE 802.11a conformable wireless local area networks by a MIMO system with two transmit and two receive antennas. For this application, the new soft detector is about 10 times faster than the LSD-based one and is about 10 times slower than the LS-based one. Yet the packet error rate due to using the new soft detector is quite close to that of using the LSD-based one.
Highlights
High transmission data rate is of particular importance for future wireless communication services
At the cost of some performance degradation, the LSDbased soft detector improves the computational efficiency of the space-time bit-interleaved coded modulation (STBICM) detector significantly due to limiting the search over the much smaller sets. (We do not know the exact degradation for our wireless local area networks (WLANs) application since the STBICM detector is too slow to make a reasonable comparison.) the list sphere decoder (LSD)-based soft detector is not as efficient as sphere decoder (SPD) due to the following reasons: (a) LSD in Step SD1 uses fixed sphere radius whereas SPD uses changing sphere radius that shrinks with the finding of a new point in the sphere with a shorter distance and (b) the bit metric calculation in Step SD2 needs additional computations
Our results obtained under the flat fading channel condition can be readily extended to the orthogonal frequency-division multiplexing (OFDM)-based WLAN systems operating over frequency-selective fading channels [21]
Summary
High transmission data rate is of particular importance for future wireless communication services. The performance of this detector can be poor, especially when the channel matrix is illconditioned The latter has a performance close to that of STBICM with a significantly improved computational efficiency; it is based on the STBICM principle but searches in a small sphere, via modifying the sphere decoder (SPD), which is a hard detector [12]. The poor performance of the LSbased soft detector is mainly due to providing poor soft information to the Viterbi decoder as a result of the channel matrix being ill-conditioned. Whenever this happens, we use the LSD-based soft detector in the new hybrid soft detector; otherwise, we use the LS-based one.
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