MIMO-OFDM (original) (raw)
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This paper proposes a space-frequency (SF) coding scheme for non-coherent (NC) Multiple Input Multiple Output (MIMO)-Orthogonal Frequency Division Multiplexing (OFDM) fading links, where neither the transmitter nor the receiver knows the channel. Our strategy consists in applying a convolutional encoder and an interleaver before applying a SF encoder. This SF encoder distributes the encoded and interleaved bits over the different OFDM symbols. In order to reduce the decoding complexity, each OFDM symbol is divided into several groups. Within each group, the obtained bits are broken into two substreams. The first substream is used to construct a systematic NC codeword which leads to a simple decoding rule over the multipath channel. The second subtream is mapped to a Grassmannian NC codeword obtained via an exponential map and that was proposed for NC space-time (ST) coding based system and has the advantage of using all the degrees of freedom of this system. We show through asymptotic Pairwise Error Probability (PEP) analysis and simulation results that our encoding strategy can provide full diversity gain and achieves better performance in terms of spectrum efficiency and bit error rate than both the systematic NC-SF coding and our proposed SF coding without convolutional encoding and interleaving.
An efficient space-frequency coding scheme over unknown frequency-selective fading channels
This paper investigates space-frequency (SF) coding for non-coherent (NC) Multiple Input Multiple Output (MIMO)-Orthogonal Frequency Division Multiplexing (OFDM) fading links, where neither the transmitter nor the receiver knows the channel. Our strategy consists in distributing the convolutional encoded and interleaved bits over the different transmit antennas, OFDM tones and OFDM symbols. The combination of the convolutional coding and bit interleaving with the SF coding can exploit the maximum spatial/frequency diversity over frequency-selective channels. In order to reduce the decoding complexity, we divide the OFDM symbol into several groups and apply differential encoding and decoding between adjacent groups. The proposed NC SF matrix is designed as a combination of a differential Cayley code and a systematic NC SF code, which leads to a simple decoding rule over the multipath channel. We show through asymptotic Pairwise Error Probability (PEP) analysis and simulation results that our encoding strategy can provide full diversity gain and achieves better performance in terms of spectrum efficiency and symbol error rate than all three the systematic NC-SF coding, the Cayley differential SF coding and our proposed SF coding without convolutional encoding and bit interleaving.
Unitary and Non-Unitary Differential Space-Frequency Coded OFDM
2008 Ieee Wireless Communications and Networking Conference, 2008
In this paper, we present the code design structure of unitary and non-unitary differential space-frequency group codes (DSFCs) for multiple-input multiple-output (MIMO)orthogonal frequency division multiplexing (OFDM) systems based on optimal coherent space-frequency (SF) group codes. Under the assumption that the transmitter knows only the delay profile of the channel, a differential transmission rule incorporated with subcarrier allocation is obtained that allows data to be sent without channel estimates at the transmitter or receiver. The differential encoding/decoding is performed in the frequency domain within each single OFDM symbol. Therefore, proposed DSFCs can be successfully decoded even for a rapidly fading channel which may change independently from one OFDM symbol to another. Unitary and nonunitary DSFCs, that are constructed based on design criteria, are compared with recently published techniques in the literature and shown to inherit coding gain of optimal coherent SF codes. Due to design structure and energy constraints, our nonunitary DSFCs do not blow up or diminish during the differential encoding.
2008
In this paper, we propose a noncoherent spacefrequency (SF) code for multiple-input-multiple-output (MIMO) orthogonal-frequency-division-multiplexing (OFDM) systems for broadband wireless communications. The proposed noncoherent SF code matrix is constructed as a combination of a noncoherent SF code matrix and a differential modulation matrix. Comparing to noncoherent SF codes and differential SF codes in the literature, the advantages of our proposed code are higher spectrum efficiency, no error floor and more suitable for broadband communication systems. Taking advantage of the codeword structure of the proposed SF code, we devise a two-stage decoding scheme, in which the decoding process is implemented in two steps by decoding the component noncoherent codeword matrix and the component differential codeword matrix sequentially. Accordingly, the decoding scheme efficiently reduces decoding complexity. Simulation results show that our proposed scheme with two-stage decoding yields better performance than the noncoherent SF codes and frequency-domain differential codes proposed in the literature.
Group-based Noncoherent Space-Frequency Codes and Efficient Decoding
2008
In this paper, we focus on noncoherent spacefrequency (SF) coded multiple-input-multiple-output orthogonalfrequency-division-multiplexing (MIMO-OFDM) systems. Based on OFDM subcarrier grouping, a group-based unitary spacefrequency code is proposed and the effect of grouping on system performance is studied. Comparing to the coding scheme without grouping, which implements SF coding among all the OFDM tones, the proposed group-based coding scheme can greatly reduce the decoding complexity, making the noncoherent SF codes more applicable to practical use. By relating the noncoherent SF codes with packings in Grassmann manifold, we propose an efficient decoding method by restricting the implementation of decoding within a subset of the codebook. Numerical results are presented to demonstrate and verify our proposals.
PHY 12-4 - Unitary and Non-Unitary Differential Space-Frequency Coded OFDM
2008 IEEE Wireless Communications and Networking Conference, 2008
In this paper, we present the code design structure of unitary and non-unitary differential space-frequency group codes (DSFCs) for multiple-input multiple-output (MIMO)orthogonal frequency division multiplexing (OFDM) systems based on optimal coherent space-frequency (SF) group codes. Under the assumption that the transmitter knows only the delay profile of the channel, a differential transmission rule incorporated with subcarrier allocation is obtained that allows data to be sent without channel estimates at the transmitter or receiver. The differential encoding/decoding is performed in the frequency domain within each single OFDM symbol. Therefore, proposed DSFCs can be successfully decoded even for a rapidly fading channel which may change independently from one OFDM symbol to another. Unitary and nonunitary DSFCs, that are constructed based on design criteria, are compared with recently published techniques in the literature and shown to inherit coding gain of optimal coherent SF codes. Due to design structure and energy constraints, our nonunitary DSFCs do not blow up or diminish during the differential encoding.
Diversity and Coding Gains of Space-Time-Frequency Coded MIMO-OFDM
VTC Spring 2008 - IEEE Vehicular Technology Conference, 2008
Space-time-frequency (STF) coding for multipleinput multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) over frequency-selective Rayleigh fading channels is considered. The maximum diversity order and coding gain of the system are derived when linear constellation precoding (LCP) is applied to OFDM symbols. It is also shown that with a proper subcarrier grouping of the OFDM symbols, the system implementation can be greatly simplified while maintaining the diversity order and coding gain. In particular, as long as the group size F is not less the number of effective resolvable channel taps L, the maximum diversity order can always be achieved. Moreover, if F ≥ L, and F is an Euler number or an integer power of 2, the maximum coding gain can be achieved. Otherwise, the achievable coding gain approximates 70% of the maximum one.
Experimental studies on optimal space-frequency codes for MIMO-OFDM systems
Conference Record of the Thirty-Eighth Asilomar Conference on Signals, Systems and Computers, 2004.
In this paper, we test the performance of optimal space-frequency code (SFC) [5] in multiple input multiple output (MIMO) orthogonal frequency division multiplexing (OFDM) communication system on Stevens Wireless Testbed. As a comparison, we also test the performance of single input single output (SISO) system and MIMO system with simple transmit delay diversity in the same frequency-selective fading environment. All the implementations are based on IEEE 802.11 standards. The experimental results shows that optimal space-frequency code is robust against the impairments of practical system.