Daisei Uchida

A new signal detection scheme combining ZF and K-best algorithms for OFDM/SDM

This paper proposes a new signal detection scheme that combines zero-forcing (ZF) and K-best algorithms for orthogonal frequency division multiplexing with space division multiplexing (OFDM/SDM) systems. Among various signal detection algorithms for SDM signals, maximum likelihood detection (MLD) is one of applicable approaches, which achieves the optimal performance. However, it suffers from exponential computational complexity against the number of transmit antennas and modulation order. Thus, we consider the K-best algorithm for the reduction of the computational complexity. We proposed the modified K-best algorithm, which exploits the ZF algorithm for initial symbol estimation. The initial symbol estimation improves the decoding accuracy of the original K-best algorithm. Therefore, the proposed scheme achieves both the reduction of the MLD algorithms computational complexity and the improvement of the original K-best algorithms decoding accuracy. Computer simulation results show that the performance degradation from the MLD algorithm is suppressed to just 1 dB or so in the required E/sub b//N/sub o/ for packet error rate (PER) = 10/sup -2/, when either 16 quadrature amplitude modulation (16QAM) or 64QAM is applied with three transmit and three receive antennas. In these cases, about 87% and 99% fewer metric computations are required than the MLD algorithm, respectively. It is presented that the proposed algorithm offers significant reduction of the computational complexity compared to the MLD algorithm.

A new synchronization scheme for packet mode OFDM-SDM signals in wireless LAN

This paper proposes a new synchronization scheme for packet mode orthogonal frequency division multiplexing (OFDM) signals employing space division multiplexing (SDM); it targets IEEE 802.11 TGn wireless LANs that offer over 100 Mbit/s. In addition, this paper shows the packet format of OFDM-SDM signals that ensures backward compatibility with IEEE 802.11a. The proposed synchronization scheme has simple open-loop construction and consists of automatic frequency control (AFC), symbol timing detection, channel estimation and phase tracking. The AFC and symbol timing detection are carried out in the time-domain. After OFDM demodulation, the proposed scheme processes channel estimation and phase tracking in the frequency-domain. Considering all the above synchronization tasks, we evaluate the packet error rate (PER) performance using the TGn-defined multi-input multi-output (MIMO) channel model. The proposed scheme shows superior performance; it suppress the required Eb/N0 degradation to within 0.4 dB (0.3 dB) with 64 byte (1000 byte) packets compared to the performance achieved if only channel estimation is considered; the RMS delay spread = 50ns.

A Short-burst Synchronization Method for Narrowband Wireless Communication Systems

This paper proposes a new burst synchronization method that improves transmission efficiency. This method suits narrowband wireless communications systems, whose traffic is dominated by short packets such as radio-frequency identification (RF-ID) information. In these systems, overhead symbols such as preamble and pilot symbols degrade the transmission efficiency. The proposed method eliminates preamble symbols and reserves pilot symbols for accurate burst synchronization. The proposed coded pilots enable frame acquisition, carrier recovery, and phase tracking to be achieved with coherent detection. Computer simulation results show that the proposed method achieves up to 26% better transmission efficiency, while achieving better packet error-rate performance than conventional methods

Inter-eigenbeam interleaving scheme for eigenbeamspace division multiplexing in OFDM system

This paper proposes an inter-eigenbeam interleaving scheme for the eigenbeam-space division multiplexing (E-SDM) in orthogonal frequency division multiplexing (OFDM) systems. It changes the assignment of eigenbeams to each data stream under the rule of cyclic sub-carrier selection, and the signal error created by eigenbeams with small eigenvalues can be corrected by a forward error correction (FEC) scheme that involves the eigenbeams with large eigenvalues. We evaluate the throughput performance of the proposed scheme and compare it with adaptive bit loading and transmission power control (ABL/TPC), which is a conventional E-SDM scheme. The simulation results show that the proposed scheme offers more stable throughput performance than ABL/TPC under fast Doppler fading environments. Keywords-component; MIMO, SDM, Eigenbeam, OFDM

Hierarchical ICI canceller for a novel SDM-COFDM Scheme

This paper proposes a hierarchical ICI (inter-channel interference) canceller to improve packet error rate performance of a novel SDM (space division multiplexed) -COFDM (coded orthogonal frequency division multiplexing) scheme. This ICI canceller comprises two types of ICI cancellers, a conventional multiplicative ICI canceller and a newly proposed subtractive ICI canceller. Moreover, we also employ the packet error detectors and the selectors to the hierarchical ICI canceller. According to the error detection result from the error detectors, the selectors select the correct packets among the outputs of the multiplicative and subtractive ICI cancellers. Computer simulation results show that with a subcarrier modulation scheme of 64QAM and a coding rate of 3/4, the proposed hierarchical ICI canceller improves the required CNR (carrier to noise power ratio) by 2.3 dB compared to that by the conventional multiplicative ICI canceller at a PER of 10/sup -2/in a fading environment.

Experimental evaluation of SDM-COFDM using hierarchical ICI canceller with pilot-based channel tracking in fast multipath fading

We develop an SDM (space division multiplexed)-COFDM (coded orthogonal frequency division multiplexing) prototype using a hierarchical ICI canceller with a pilot-based channel tracking scheme. We evaluate the experimental performance of the prototype when the subcarrier modulation scheme is 16QAM, the coding rate is 3/4 and the maximum Doppler frequency is 50 Hz in the 5 GHz band. PER performance with the channel tracking scheme is dramatically improved compared to those without the channel tracking scheme. PER degradation compared with the case when the pilot symbol interval is 3, which is the best case, at PER of 0.1 was less than 2 dB when the pilot symbol interval was less than 93. We calculate the throughput considering the overhead caused by the preamble and pilot signals for channel tracking and found that the pilot symbol interval that provides the optimum throughput ranges from 48 to 60, which depends on CNR.

Experimental performance evaluation of SDM-COFDM prototype using hierarchical ICI canceller for MIMO-based broadband wireless access systems

This paper introduces experimental performance evaluation of SDM-COFDM (space division multiplexed-coded OFDM) prototype employing a hierarchical ICI canceller for MIMO-based broadband wireless access systems. The prototype has two types of ICI cancellers, multiplicative and subtractive, to obtain diversity gain. The multiplicative canceller multiplies the received signals by the estimated inverse propagation coefficient matrix. In addition, the subtractive canceller generates ICI replicas, subtracts the replicas from the received symbols, weights the subtracted signals by the estimated propagation coefficients, and combines them to obtain diversity gain. In this paper, the PER (packet error rate) performance of the prototype is evaluated by experiments in frequency selective fading environments. The experimental results quantitatively indicate the required CNR (carrier to noise power ratio) improvements by the hierarchical canceller from only the multiplicative canceller, on the variable conditions of the fading parameters such as delay spread and maximum Doppler frequency.

New CDM-type diversity scheme for broadband MIMO-OFDM system

The paper proposes a new code division multiplexing (CDM)-type diversity scheme for broadband multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) system. The scheme performs spectrum spreading and despreading using orthogonal spreading codes for multiple transmitting and receiving antennas, and achieves frequency diversity gain by combining despread data. When changing a transmission bit rate by changing the baseband bit rate, or the number of antennas, without changing air interface parameters, such as the OFDM parameters, the proposed scheme just needs to change the spreading factor. In that respect, the proposed scheme has the advantage over the space-time coding (STC)-type diversity scheme which needs to change the STC encoder and decoder in the same case. We evaluated the performance of the proposed diversity scheme in frequency selective fading environments by computer simulation. The 2/spl times/1 proposed diversity scheme had a diversity gain of 1.6-3.2 dB, which is comparable gain to the 2/spl times/1 STC-type transmission diversity scheme in wireless LAN environments.