Hangjun Chen

Iterative estimation and cancellation of clipping noise for OFDM signals

Clipping is an efficient and simple method to reduce the peak-to-average power ratio (PAPR) of orthogonal frequency division multiplexing (OFDM) signals. However, clipping causes distortion and out-of-band radiation. In this letter, a novel iterative receiver is proposed to estimate and cancel the distortion caused by clipping noise. The proposed method is applied to clipped and filtered OFDM signals. It is shown by simulation that for an IEEE 802.11a typical scenario the system performance can be restored to within 1 dB of the nonclipped case with only moderate complexity increase and with no bandwidth expansion.

Turbo space-time codes with time varying linear transformations

Turbo space-time codes with symbols precoded by randomly chosen unitary time variant linear transformations (TVLT) are investigated in this paper. It is shown that turbo codes with TVLT achieve full diversity gain and do not require exhaustive tests of the rank criterion. We prove that the coding gain performance of turbo space-time codes with TVLT improves with the Hamming distance between codewords (number of different columns). As an additional benefit of the application of TVLT, with the removal of the constant modulation condition, we prove that throughput rates achieved by these codes are significantly higher than those for conventional space-time codes. Numerical results are provided to demonstrate diversity gains, coding gains and rates of turbo space-time codes with TVLT

An iterative method to restore the performance of clipped and filtered OFDM signals

Clipping is an efficient and simple method to reduce the peak-to-average power ratio (PAPR) of OFDM signals. However, clipping causes distortion and out-of-band radiation. In this paper, a novel iterative receiver is proposed to estimate and cancel the distortion caused by clipping noise. The proposed method is applied to clipped and filtered OFDM signals. It is shown by simulation that for an 802.11a system, the PAPR can be reduced to as low as 4 dB while the system performance can be restored to within 1 dB of the non-clipped case with only moderate complexity increase and with no bandwidth expansion.

EXIT charts for turbo trellis-coded modulation

In this letter, we extend the previously proposed extrinsic information transfer charts (EXIT) method to the analysis of the convergence of turbo codes to turbo trellis-coded modulation (TTCM) schemes. The effectiveness of the proposed method is demonstrated through examples. The proposed method provides a convenient way to systematically compare between schemes and thus can be used as a tool in the design of TTCM.

Layered turbo space-time coded MIMO-OFDM systems for time varying channels

A joint detection-estimation scheme is proposed for multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) systems. The transmitter employs a layered turbo space-time code. The iterative scheme proposed for the receiver integrates in one scheme turbo decoding, co-antenna interference suppression and channel estimation. A main observation is that the high coding gain of the turbo space-time code can compensate for the application of a simple co-antenna interference suppression scheme and can also facilitate good channel estimates. The performance of the MIMO-OFDM system is validated by simulations under various channel conditions, including high Doppler. Numerical results show that for a 4 transmit 4 receive antenna (4T4R) system, with a data rate of 4 Mb/s over a 1.25 MHz bandwidth, a packet error rate (PER) of 10/sup -2/ is achieved at a signal-to-noise ratio (SNR) of 16 dB for a typical urban channel with Doppler frequencies as high as 200 Hz. For a 4T6R system, the same performance can be achieved for only 6 dB SNR.

Parallel concatenated turbo multiple antenna coded modulation: principles and performance†

A channel-coding scheme is introduced that features parallel concatenated recursive systematic codes with multilevel modulation and multiple transmit/receive antennas. The proposed scheme is a type of turbo space–time codes and is referred to as turbo multiple antenna coded modulation (turbo-MACM). Turbo-MACM combines the advantages of powerful turbo codes with the transmit/receive diversity of multiple antenna coded modulation. The scheme utilizes recursive and systematic constituent codes and features full rate and, as demonstrated by simulations, full spatial diversity. An iterative symbol-by-symbol maximum a posteriori (MAP) algorithm operating in the log domain is developed for decoding turbo-MACM. Simulation results are provided for 4-PSK and 8-PSK schemes over the block-fading channel. It is shown that the scheme provides an advantage of 3 to 5 dB over conventional space–time codes of comparable complexity. Copyright

Layered MIMO scheme with antenna grouping

In this paper we extend our previously proposed layered turbo coded multiple-input multiple-output (MIMO) scheme by introducing new techniques to improve the design of the transmitter and the receiver. These MIMO systems feature two antenna per layer with random antenna grouping, which reduces interference between layers. And multidimensional set partition is applied to encoder design to improve the coding gain. Based on these design techniques, the receiver only uses simple parallel interference cancellation (PIC) with spatial matched filtering (SMF) to separate the signals from different layers. It is shown that the performance of the proposed scheme is within 2 dB of outage capacity and is similar or better than other proposed MIMO schemes using more sophisticated interference suppression techniques.

Error performance analysis of multilevel turbo-code with antenna diversity

A channel coding scheme is analyzed that features parallel concatenated systematic space-time codes with multilevel modulation and multiple transmit/receive antennas. The scheme is referred to as turbo space-time coded modulation (turbo-STCM). It combines the advantages of turbo codes with the diversity of space-time codes. The scheme features full diversity and full rate. We also extend turbo-STCM to the case of large numbers of antennas (>2). Simulation results are provided over the block-fading channel. It is shown that this turbo scheme provides an advantage of 1.1 dB over conventional space-time codes of similar decoding complexity. The analytical union bound of the bit error probability is derived for turbo-STCM over the Rayleigh block-fading channel. The bound makes it possible to express the performance analysis of turbo-STCM in terms of the properties of the constituent space-time codes. The union bound is demonstrated for 8-PSK turbo-STCM with two transmit antennas and one or two receive antennas.

Successive packing based interleaver design for turbo codes

The interleaver is the key component in both turbo encoder and decoder. It has been shown that good turbo code performance can be obtained by using a pseudo-random interleaver. However, it is difficult to analyze the corresponding pseudo-random algorithms such that the performance can be guaranteed, and furthermore they are computationally expensive. We focus on a deterministic turbo code interleaver design. A novel successive packing (SP) based turbo code interleaver design method is proposed. In this method, the interleaver is generated based on iterative packing of the basis interleaver. We have shown that SP based interleavers possess the following desirable features: prunability; adaptability to various criteria; pseudo-random distribution. Simulation results demonstrate the superior performance of SP over other deterministic interleaver design techniques.