2 research outputs found
Distributed space-frequency coding for cooperative diversity over broadband relay channels with DF relaying
Multipath fading is one of the main challenges in transmission over wireless broadband relay channels due to frequency selectivity, which may deteriorate the received signal. Exploiting the extra source of multipath diversity, aside from cooperative (user) diversity, is important when coping with these wireless channel limitations. In this correspondence, we propose a new distributed space-frequency code (SFC) for broadband fading relay channels that can exploit both the spatial and multipath diversities in a distributed fashion. An upper bound for pairwise error probability (PEP) is derived, and from this PEP bound, we show that the proposed code achieves a diversity of order NL, where N is the number of relay nodes, and L is the channel memory length. The decode-and-forward (DF) protocol and erroneous decoding at the relay nodes are considered. Moreover, it is shown that the proposed code structure achieves the maximum coding gain among the linearly coded systems over channels with uniform power delay profiles
New OFDM schemes based on orthogonal transforms for mobile communications systems :
PhD ThesisIn this thesis, two new orthogonal frequency division multiplexing (OFDM)
systems are presented. The first scheme proposes a new OFDM system
transceiver based on the C-transform, which is termed C-OFDM. Over
multipath channels, the C-OFDM achieves 10 dB signal-to-noise ratio
(SNR) gain at 10−4 bit-error-rate (BER), in comparison to the OFDM
that based on the is discrete cosine transform (DCT-OFDM) and the
conventional OFDM schemes. It also reduces the peak-to-average power
ratio (PAPR) of the OFDM signal by about 1 dB and in some cases
up to 3 dB. In the second scheme, a new fast, orthogonal X-transform
is produced. The proposed X-transform is then used in a new OFDM
named X-OFDM to greatly reduce the complexity, the PAPR and the
BER. The proposed scheme achieves around 15 dB SNR gain in comparison
to the conventional OFDM at 10−4 BER and reduces the average
PAPR (over 105 OFDM symbol) by about 6 dB for N =1024 subcarriers.
Furthermore, in this study, the X-transform is utilized to produce a new
Alamouti space-time OFDM (ST-OFDM). The proposed ST-X-OFDM
scheme reduces the transmitter complexity and achieves important SNR
gain over the conventional ST-OFDM systems. The BER performance
of the proposed schemes in the presence of solid-state power amplifiers
(SSPAs) is also investigated analytically and by simulation. It shows that
the X-OFDM is resilient to the SSPAs nonlinear distortion whereas the
C-OFDM may lead to BER impairment in the presence of the SSPA.
Furthermore, a coding technique to mitigate the sensitivity of the COFDM
scheme to the SSPA is also proposed in this study.
In this research, mathematical models for the proposed C-OFDM, XOFDM
and ST-X-OFDM, which tightly match the simulation results
over a diverse range of transmission scenarios and mapping schemes,
are also derived. In addition, the BER performance of the proposed COFDM
and X-OFDM schemes in the presence of the carrier frequency
offset (CFO), with and without frequency synchronization algorithm,
are also investigated. The proposed C-OFDM and X-OFDM schemes
are more sensitive to the CFO than the conventional schemes. However,
when frequency synchronization algorithm is used, both the proposed
schemes retain their significant BER improvement in comparison to the
conventional schemes.Ministry of Higher Education
and Scientific Research (MOHSR), Iraq and to the Iraqi cultural attach-
London for supporting me financially during my study in England