Agus Santoso

Interference Cancellation in Coexisting Wireless Local Area Networks

The interference in coexisting wireless local area networks (WLANs), can be viewed as a layered space-time (LST) structure, in which the number of access points (APs) is equal to the number of transmit antennas. Thus, the interference that is caused by APs from different vendors is equivalent to the interference between transmit antennas in LST architecture. This analogy can be further extended to the WLANs receiver strategy, so that receiver structures derived for LST architectures can be directly applied to mitigate against the interference between vendors. Therefore, in this paper, we propose the LST architecture receivers in the physical layer (PHY) to mitigate against the interference in coexisting WLANs. To improve the bit error rate (BER) performance further, a cross-layer design in both the PHY and medium access control (MAC) layers is also proposed. It is shown that the proposed receivers demonstrate superior performance to the standard receiver for WLANs

A chip level decision feedback equalizer for CDMA downlink channel with the Alamouti transmit diversity scheme

In commercial wideband code division multiple access (W-CDMA), the transmitted signal in the downlink channel is spread by orthogonal codes. However, frequency selective fading destroys the orthogonality, which causes multiple access interference (MAI). Although the RAKE receiver can exploit path diversity, it does not restore the orthogonality and suppress the MAI. As a result, CDMA becomes an interference limited system. The equalization followed by despreader can be adopted to restore the orthogonality and then to suppress the MAI, without significantly increasing the complexity. In this paper, we propose to apply a chip level decision feedback equalizer (DFE) with the Alamouti transmit diversity scheme to restore the orthogonality of the received spreading sequences. Theoretical and simulation results show significant performance gains compared to the chip level linear equalizer (LE) and the RAKE receiver.

The Code Design of the Space-time Trellis Codes with Dynamic Transmit Power Allocation

Space-time trellis codes (STTCs) have been shown to efficiently use transmit diversity to improve the error performance. In existing space-time trellis codes, the transmit power is equally distributed across all transmit antennas. However, this power allocation strategy is not optimum regarding the error performance. In this paper, we propose a design of space-time trellis codes with dynamic transmit power allocation (STTCs/DTPA), when partial channel state information (CSI) is available at the transmitter side. It is demonstrated that this new scheme can achieve a full diversity order and have much better error performance than the standard STTCs scheme, the existing STTCs/DTPA, and some other closed-loop transmit diversity schemes with partial CSI

Dynamic Transmit Power Allocation in Space-Time Trellis Coded Systems

Space-time trellis codes (STTCs) have been shown to efficiently use transmit diversity to improve error performance. In existing STTCs, the transmit power is equally distributed across all transmit antennas. In fact, when feedback information is available at the transmitter, the equal power allocation strategy is not optimum regarding the error performance. In this paper, we propose a new scheme, referred to as space-time trellis codes with dynamic transmit power allocation (STTCs/DTPA), when partial channel state information (CSI) is available at the transmitter. A closed-form pairwise error probability (PEP) upper bound is derived. The optimum power allocation scheme and the code design criteria, based on the PEP upper bound, are proposed. Theoretical and simulation results show that the proposed scheme performs much better in terms of error probability than the general open-loop STTCs and other closed- loop transmit diversity schemes. For example, the new 16-state STTCs/DTPA scheme is 5.6 dB better than the standard 16-state Chen/Yuan/Vucetic code for three transmit antennas.

Dynamic Transmit Power Allocation Scheme for Space-Time Turbo Trellis Codes with Partial CSI Feedback

Space-time turbo trellis coding (STTuTC) has been shown to provide a significant performance improvement over comparable space-time trellis coding (STTC) schemes due to an increase in coding gain. In conventional STTuTC schemes equal power is allocated to each transmit antenna. From information theory we know that if partial or full channel state information (CSI) is available at the transmitter, the system performance can be further improved. In this paper we consider the design of a STTuTC scheme where the transmitter has knowledge of the order of channel quality for each transmit antenna. For the proposed scheme, the transmitter allocates the transmit power to each antenna based on this information. A closed-form expression for the pair-wise error probability (PEP) upper bound over quasi-static Rayleigh fading channels is derived. The optimum power allocation coefficients are calculated based on this PEP bound. Simulation results show a significant frame error rate (FER) performance improvement for the proposed scheme with optimal power allocation compared to the conventional STTuTC scheme with equal power allocation

Dynamic transmit power allocation strategy for space-time trellis coded systems

Space-time trellis codes (STTCs) have been shown to efficiently use the transmit diversity to improve the error performance. In the existing STTCs, the transmit power is equally distributed across all the transmit antennas. However, this power allocation strategy is not optimum with regards to the error performance. We propose a new scheme, referred to as the space-time trellis codes with dynamic transmit power allocation (STTCs/DTPA), when partial channel state information (CSI) is available at the transmitter side. It is demonstrated that this scheme can achieve a full diversity order and have much better performance than general STTC schemes in error probability.