COFDM

White LEDs are set to penetrate many areas of everyday life. An interesting property of these devices (in addition to their lightening capabilities) is that they can be utilised for data transmission. In the past, primarily OOK (on-off keying) has been used for digital data modulation of such devices. OOK imposes limitations on the achievable data rates. Therefore, in this paper OFDM is considered in combination with higher order modulation schemes. A hardware demonstrator with an entire link chain (transmitter and receiver) is developed and measured BER (bit error ratio) results are reported. The system uses pilot sub-carriers to correct frequency synchronisation errors, training sequences for channel estimation and time synchronisation routines. Forward error correction (FEC) coding is used. It is shown that for COFDM (coded OFDM) with QPSK (quadrature phase shift keying) modulation and a single LED, a BER of 2 times 10-5 is achieved for a distance of 90 cm between transmitter and...

- In this paper a new scheme is proposed for progressive
image transmission over coded Orthogonal Frequency Division
Multiplexing (OFDM) system with Low Density Parity Check
Coding (LDPC). Trigonometric transforms are used in this
scheme for improving the performance of the OFDM systems
and reducing the PeakTo- Average Power Ratio (PAPR) of
OFDM signal. It improves the error resilience ability and
transmission efficiency for progressive image transmission over
Additive White Gaussian Noise (A WGN) channel. The Set
Partitioning In Hierarchical Trees (SPIHT) algorithm is used for
source coding of the images to be transmitted. In the proposed
scheme the transmit data sequence of the OFDM signal after
Inverse Fast Fourier Transform (lFFT) is grouped into in-phase
and in-quadrature components, then each component is
transformed using either the Discrete Cosine Transform (DCT)
or the Discrete Sine Transform (DST). The simulation results
show that adding the DST to the system improves the visual
quality of reconstructed images and reduces the PAPR of OFDM
signal more than the DCT.

In this paper, we discuss and present simulation results for the performances of COFDM systems using turbo codes and operating in a mobile radio environment. Results show that the echo power has a much stronger influence than the guard time interval or echo delay. This scheme is shown to be an excellent solution for transmission over bandlimited mobile channels.

The performances of a multicarrier modulation (COFDM) system in an urban mobile radio channel is analyzed using a computer-aided analysis tool called SPW. This multicarrier modulation system, with convolutional coding and interleaving, provides an extremely bandwidth efficient and multipath resistant transmission method. COFDM gives a remarkable performance in selective Rayleigh channels at a much higher bit rate than conventional systems

The design of a blind receiver for coded orthogonal frequency-division multiplexing (OFDM) communication systems in the presence of frequency offset and frequency-selective fading is investigated. The proposed blind receiver iterates between a Bayesian demodulation stage and a maximum a posteriori (MAP) channel decoding stage; and the extrinsic a posteriori probabilities of data symbols are iteratively exchanged between these two stages to achieve successively improved performance. The Bayesian demodulator computes the a posteriori data symbol probabilities, based on the received signals (without knowing or explicitly estimating the frequency offset and the fading channel states), by using Markov chain Monte Carlo (MCMC) techniques. In particular, two MCMC methods, namely, the Metropolis-Hastings algorithm and the Gibbs sampler, are studied for this purpose. Computer simulation results show that the proposed Bayesian blind turbo receiver can achieve good performance and it is robust against modeling mismatch

In this paper a new scheme is proposed for progressive image transmission over coded Orthogonal Frequency Division Multiplexing (OFDM) system with Low Density Parity Check Coding (LDPC). Trigonometric transforms are used in this scheme for improving the performance of the OFDM systems and reducing the PeakToAverage Power Ratio (PAPR) of OFDM signal. It improves the error resilience ability and transmission efficiency for progressive image transmission over Additive White Gaussian Noise (A WGN) channel. The Set Partitioning In Hierarchical Trees (SPIHT) algorithm is used for source coding of the images to be transmitted. In the proposed scheme the transmit data sequence of the OFDM signal after Inverse Fast Fourier Transform (lFFT) is grouped into in-phase and in-quadrature components, then each component is transformed using either the Discrete Cosine Transform (DCT) or the Discrete Sine Transform (DST). The simulation results show that adding the DST to the system improves the visu...