Achievable diversity order by space-time trellis coding combined with MLED and OFDM over frequency selective fading channels.
ABSTRACT Space-time trellis code (STTC) in frequency selective fading channel using maximum likelihood equalization and detection (MLED), and orthogonal frequency division multiplexing (OFDM) are compared in this paper for channels with arbitrary delay profile. The performance bound for both schemes are first derived and their performances are compared both analytically and through simulations. Code design, receiver complexity, interleaver design and the robustness issues are addressed in these comparisons
Conference Paper: Space-time code design in OFDM systems[Show abstract] [Hide abstract]
ABSTRACT: We consider a space-time coded (STC) orthogonal frequency-division multiplexing (OFDM) system in frequency-selective fading channels. By analyzing the pairwise error probability (PEP), we show that STC-OFDM systems can potentially provide a diversity order as the product of the number of transmitter antennas, the number of receiver antennas and the frequency selectivity order, and that the large effective length and the ideal interleaving are two most important principles in designing STCs for OFDM systems. Following these principles, we propose a new class of trellis-structured STCs. Compared with the conventional space-time trellis codes, our proposed STC's significantly improve the performance by efficiently exploiting both the spatial diversity and the frequency-selective-fading diversityGlobal Telecommunications Conference, 2000. GLOBECOM '00. IEEE; 02/2000
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ABSTRACT: Multiuser orthogonal frequency division multiplexing (OFDM) with adaptive multiuser subcarrier allocation and adaptive modulation is considered. Assuming knowledge of the instantaneous channel gains for all users, we propose a multiuser OFDM subcarrier, bit, and power allocation algorithm to minimize the total transmit power. This is done by assigning each user a set of subcarriers and by determining the number of bits and the transmit power level for each subcarrier. We obtain the performance of our proposed algorithm in a multiuser frequency selective fading environment for various time delay spread values and various numbers of users. The results show that our proposed algorithm outperforms multiuser OFDM systems with static time-division multiple access (TDMA) or frequency-division multiple access (FDMA) techniques which employ fixed and predetermined time-slot or subcarrier allocation schemes. We have also quantified the improvement in terms of the overall required transmit power, the bit-error rate (BER), or the area of coverage for a given outage probability.IEEE Journal on Selected Areas in Communications 06/2001; · 3.12 Impact Factor
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ABSTRACT: This paper studies the performance of two major space-time trellis code (STC) transmission and detection schemes over frequency selective fading channels: (1) maximum likelihood equalization and detection (MLED), and (2) orthogonal frequency division multiplexing (OFDM). Their performance is evaluated and compared both analytically and empirically. It shows that the maximum achievable diversity order for MLED and OFDM approaches are both identical as NML, where N, M is the number of transmit and receive antennas respectively, and L is the channel tap length. To achieve a certain amount of diversity order, the MLED approach requires a weaker code, but the decoding trellis complexity for both MLED (with combined trellis detector) and OFDM are the same. For codes that do not achieve the maximum diversity order, MLED always achieves higher diversity order than OFDM. Moreover, the use of interleaver in STC OFDM is essential in avoiding rank deficiency caused by clustering of path arrivals, which reduces the diversity order of the system. Simulation results support these arguments, and show that the MLED approach outperforms OFDM when the same maximum diversity order achievable code is used.Vehicular Technology Conference, 2002. VTC Spring 2002. IEEE 55th; 02/2002