1,859 research outputs found
TCM, TTCM, BICM and BICM-ID Assisted MMSE Multi-User Detected SDMA-OFDM Using Walsh-Hadamard Spreading
Space Division Multiple Access (SDMA) aided Orthogonal Frequency Division Multiplexing (OFDM) systems assisted by efficient Multi-User Detection (MUD) techniques have recently attracted intensive research interests. Forward Error Correction (FEC) schemes and frequency-domain spreading techniques can be efficiently amalgamated with SDMA-OFDM systems for the sake of improving the achievable performance. In this contribution a Coded Modulation (CM) assisted and Minimum Mean-Square Error (MMSE) multi-user detected SDMA-OFDM system combined with Walsh-Hadamard-Transform-Spreading (WHTS) across a number of subcarriers is proposed. The various CM schemes used are Trellis Coded Modulation (TCM), Turbo TCM (TTCM), Bit-Interleaved Coded Modulation (BICM) and Iteratively Decoded BICM (BICM-ID), which constitute bandwidth efficient schemes that combine the functions of coding and modulation. Invoking the WHTS technique is capable of further improving the average Bit Error Rate (BER) performance of the CM-SDMA-OFDM system, since the bursty error effects imposed by the frequency-domain fading encountered are spread over the entire WHT block length, therefore increasing the chances of correcting the transmission errors by the CM decoders
On the Performance of Single- and Multi-carrier Modulation Schemes for Indoor Visible Light Communication Systems
In this paper, we investigate and compare the performance of single- and
multi-carrier modulation schemes for indoor visible light communication (VLC).
Particularly, the performances of single carrier frequency domain equalization
(SCFDE), orthogonal frequency division multiplexing (OFDM) and on-off keying
(OOK) with minimum mean square error equalization (MMSE) are analyzed in order
to mitigate the effect of multipath distortion of the indoor optical channel
where nonlinearity distortion of light emitting diode (LED) transfer function
is taken into account. Our results indicate that SCFDE system, in contrast to
OFDM system, does not suffer from high peak to average power ratio (PAPR) and
can outperform OFDM and OOK systems. We further investigate the impact of LED
bias point on the performance of OFDM systems and show that biasing LED with
the optimum value can significantly enhance the performance of the system.
Bit-interleaved coded modulation (BICM) is also considered for OFDM and SCFDE
systems to further compensate signal degradation due to inter-symbol
interference (ISI) and LED nonlinearity.Comment: 6 Pages, IEEE Globecom conference 201
On Optimal Turbo Decoding of Wideband MIMO-OFDM Systems Under Imperfect Channel State Information
We consider the decoding of bit interleaved coded modulation (BICM) applied
to both multiband and MIMO OFDM systems for typical scenarios where only a
noisy (possibly very bad) estimate of the channel is provided by sending a
limited number of pilot symbols. First, by using a Bayesian framework involving
the channel a posteriori density, we adopt a practical decoding metric that is
robust to the presence of channel estimation errors. Then this metric is used
in the demapping part of BICM multiband and MIMO OFDM receivers. We also
compare our results with the performance of a mismatched decoder that replaces
the channel by its estimate in the decoding metric. Numerical results over both
realistic UWB and theoretical Rayleigh fading channels show that the proposed
method provides significant gain in terms of bit error rate compared to the
classical mismatched detector, without introducing any additional complexity
Single-RF spatial modulation requires single-carrier transmission: frequency-domain turbo equalization for dispersive channels
In this paper, we propose a broadband single-carrier (SC) spatial-modulation (SM) based multiple-input multipleoutput (MIMO) architecture relying on a soft-decision (SoD) frequency-domain equalization (FDE) receiver. We demonstrate that conventional orthogonal frequency-division multiplexing (OFDM)-based broadband transmissions are not readily suitable for the singleâradio frequency (RF) assisted SM-MIMO schemes, since this scheme does not exhibit any substantial performance advantage over single-antenna transmissions. To circumvent this limitation, a low-complexity soft-decision (SoD) FDE algorithm based on the minimum mean-square error (MMSE) criterion is invoked for our broadband SC-based SM-MIMO scheme, which is capable of operating in a strongly dispersive channel having a long channel impulse response (CIR) at a moderate decoding complexity. Furthermore, our SoD FDE attains a near-capacity performance with the aid of a three-stage concatenated SC-based SM architecture
Achievable Outage Rates with Improved Decoding of Bicm Multiband Ofdm Under Channel Estimation Errors
We consider the decoding of bit interleaved coded modulation (BICM) applied
to multiband OFDM for practical scenarios where only a noisy (possibly very
bad) estimate of the channel is available at the receiver. First, a decoding
metric based on the channel it a posteriori probability density, conditioned on
the channel estimate is derived and used for decoding BICM multiband OFDM.
Then, we characterize the limits of reliable information rates in terms of the
maximal achievable outage rates associated to the proposed metric. We also
compare our results with the outage rates of a system using a theoretical
decoder. Our results are useful for designing a communication system where a
prescribed quality of service (QoS), in terms of achievable target rates with
small error probability, must be satisfied even in the presence of imperfect
channel estimation. Numerical results over both realistic UWB and theoretical
Rayleigh fading channels show that the proposed method provides significant
gain in terms of BER and outage rates compared to the classical mismatched
detector, without introducing any additional complexity
- âŠ