3,500 research outputs found
Performance comparison of differential space-time signalling schemes for OFDM systems
Differential transmit diversity is an attractive alternative to its coherent counterpart, especially for multiple antenna systems where channel estimation is more difficult to attain compared to that of single antenna systems. In this paper we compare two different types of differential transmit diversity techniques for OFDM based transmissions. The first technique uses differential space-time block codes (DSTBC) from orthogonal designs and the second uses the differential cyclic delay diversity (DCDD). The results compare the bit error performance for several transmit antenna configurations. The results show that DCDD offers a very close performance to that of DSTBC, with the advantage of a simplified receiver structure
Spectrally efficient transmit diversity scheme for differentially modulated multicarrier transmissions
Cyclic delay diversity is a simple, yet effective, transmit diversity scheme for multicarrier based transmissions employing coherent digital linear modulation schemes. It is shown that, for satisfactory operation, the scheme requires additional channel estimation overhead compared to single antenna and traditional spaceâtime coded transmissions owing to the inherent increase in frequency selective fading. The authors analyse the additional channel estimation overhead requirement for a Hiperlan #2 style system with two transmit antennas operating in a NLOS indoor environment. The analysis shows that an additional overhead of 500% is required for the candidate system compared to a single antenna system. It is also shown that by employing differential modulation the channel estimation overhead can be eliminated with significant performance improvement compared to a system employing a practical channel estimation scheme. This novel combination, termed âdifferentially modulated cyclic delay diversity, is shown to yield a highly spectral efficient, yet simple transmit diversity solution for multi-carrier transmissions
Diversity gain for DVB-H by using transmitter/receiver cyclic delay diversity
The objective of this paper is to investigate different diversity techniques for broadcast networks that will minimize the complexity and improve received SNR of broadcast systems.
Resultant digital broadcast networks would require fewer transmitter sites and thus be more cost-effective and have less environmental impact. The techniques can be applied to DVB-T,
DVB-H and DAB systems that use Orthogonal Frequency Division Multplexing (OFDM). These are key radio broadcast network technologies, which are expected to complement emerging technologies
such as WiMAX and future 4G networks for delivery
of broadband content. Transmitter and receiver diversity technologies can increase the frequency and time selectivity of the resulting channel transfer function at the receiver. Diversity exploits the statistical nature of fading due to multipath and reduces the likelihood of deep fading by providing a diversity of transmission signals. Multiple signals are transmitted in such
a way as to ensure that several signals reach the receiver each with uncorrelated fading. Transmit diversity is more practical than receive diversity due to the difficulty of locating two receive antennas far enough apart in a small mobile device. The schemes examined here comply with existing DVB standards and can be incorporated into existing systems without change. The diversity techniques introduced in this paper are applied to the DVB-H system. Bit error performance investigations were conducted by
simulation for different DVB-H and diversity parameters
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Future transmitter/receiver diversity schemes in broadcast wireless networks
An open diversity architecture for a cooperating broadcast wireless network is presented that exploits the strengths of the existing digital broadcast standards. Different diversity techniques for broadcast networks that will minimize the complexity of broadcast systems and improve received SNR of broadcast signals are described. Resulting digital broadcast networks could require fewer transmitter sites and thus be more cost-effective with less environmental impact. Transmit diversity is particularly investigated since it obviates the major disadvantage of receive diversity being the difficulty of locating two receive antennas far enough apart in a small mobile device. The schemes examined here are compatible with existing broadcast and cellular telecom standards and can be incorporated into existing systems without change
Adaptive spatial mode of space-time and spacefrequency OFDM system over fading channels
In this paper we present a 2 transmit 1 receive (1 Tx : 1 Rx) adaptive spatial
mode (ASM) of space-time (ST) and space-frequency (SF) orthogonal frequency division
multiplexing (OFDM). At low signal to noise ratio (SNR) we employ ST-OFDM and switch
to SF-OFDM at a certain SNR threshold. We determine this threshold from the intersection
of individual performance curves. Results show a gain of 9 dB (at a bit error rate of 10-3) is
achieved by employing adaptive spatial mode compared to a fixed ST-OFDM, almost 6 dB
to fixed SF-OFDM, 4 dB to Coded ST-OFDM and 2 dB to a fixed coded SF-OFDM, at a
delay spread of 700 ns
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Measurements, processing functions and laboratory test-bed experiments for evaluating diversity in broadcast network
This paper presents a test-bed development and measurement plan for evaluating transmit diversity and on-channel repeaters in the Digital Video Broadcasting Network. Transmit diversity reduces the complexity and improves the power consumption of the personal receiving devices by enhancing the transmission of signals in NLOS cluttered environments. It is more practical than receive diversity due to the difficulty of locating two receive antennas far enough apart in a small mobile device. The on-channel repeater is to extend the coverage of the DVB-T/H network in areas where services are inaccessible by receiving the DVB-T/H signals off air, amplifying and then retransmitting it on the same frequency as received. Test service scenarios were developed to illustrate the benefits of such technologies so that effectiveness can be researched in a variety of service and terrain scenarios using purpose built test systems.The work presented in this paper was supported by the European Commission IST project PLUTO
Differential Distributed Space-Time Coding with Imperfect Synchronization
Differential distributed space-time coding (D-DSTC) has been considered to
improve both diversity and data-rate in cooperative communications in the
absence of channel information. However, conventionally, it is assumed that
relays are perfectly synchronized in the symbol level. In practice, this
assumption is easily violated due to the distributed nature of the relay
networks. This paper proposes a new differential encoding and decoding process
for D-DSTC systems with two relays. The proposed method is robust against
synchronization errors and does not require any channel information at the
destination. Moreover, the maximum possible diversity and symbol-by-symbol
decoding are attained. Simulation results are provided to show the performance
of the proposed method for various synchronization errors and the fact that our
algorithm is not sensitive to synchronization error.Comment: to appear in IEEE Globecom, 201
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