In this paper, distributed relay diversity systems are analyzed, modeled and evaluated in an Orthogonal Frequency Division Multiplexing (OFDM) based networks. The investigated distributed relay diversity schemes exten...In this paper, distributed relay diversity systems are analyzed, modeled and evaluated in an Orthogonal Frequency Division Multiplexing (OFDM) based networks. The investigated distributed relay diversity schemes extend the ideas of a single hop transmit antenna schemes such as Cyclic Delay Diversity (CDD), Space Time Transmit Diversity (STTD), transmit Coherent Combining (CC) and Selection Diversity (SD) to distributed diversity systems. In contrast to the classical single hop system, the antennas in the distributed systems belongs to distributed relays instead of being co-located at the transmitter. The distributed relay diversity methods considered in this paper: Relay CDD (RCDD), Relay Alamouti (i.e.STTD), Relay CC (RCC) and Relay SD (RSD) are compared to the traditional 1-hop system. Analytical expressions for the received Signal to Interference Noise Ratio (SINR) are derived and used in a dynamic multi-cell multi-user simulator. Results show considerable SINR gains for both Round Robin and Max-SINR schedulers. The SINR gains translate into substantial cell throughput gains, up to 200%, compared to 1-hop systems. Despite its low complexity, the RCDD scheme has similar performance to that of other more sophisticated 2-hop schemes such as Relay Alamouti and Relay Coherent Combining. Marginally better results are observed for the Relay Selection Diversity scheme.展开更多
In orthogonal frequency division multiplexing(OFDM)system,the time variation of a wireless channel destroys orthogonality among the sub-carriers,and this induces inter-carriers interference(ICI)and degrades system per...In orthogonal frequency division multiplexing(OFDM)system,the time variation of a wireless channel destroys orthogonality among the sub-carriers,and this induces inter-carriers interference(ICI)and degrades system performance severely in mobile environment.In this paper,a new method of ICI cancellation based on delay diversity(DD)was proposed,which provides a way to mitigate the negative effect from the time variation of the wireless paths,thus improve the system performance greatly.The new method was called time-domain selfinterference cancellation(TDSIC)algorithm,which is different from other existing methods,such as frequencydomain method.In a cyclically extended OFDM system,the fading characteristics of extended OFDM symbols with different cyclic delay are different with each other,so in our TDSIC method,a new diversity collection scheme at the receiver end is proposed,which can be used to improve the system performance by suppressing ICI through selecting appropriate parameters.Moreover,the cyclically extended OFDM symbol at the transmitter side and diversity collection with different delay added OFDM symbols at the receiver side are used in the TDSIC method with the tradeoff of time-expense,so the well-known fixed delay for symbol at the transmitter side may be detected by the receiver side through estimating several parameters of wireless channels.In summary,the key of the TDSIC method is to improve the system performance with the cost of time.Based on performance analysis,simulation has proved that TDSIC may effectively improve the performance of the time-variant wireless channel.展开更多
文摘In this paper, distributed relay diversity systems are analyzed, modeled and evaluated in an Orthogonal Frequency Division Multiplexing (OFDM) based networks. The investigated distributed relay diversity schemes extend the ideas of a single hop transmit antenna schemes such as Cyclic Delay Diversity (CDD), Space Time Transmit Diversity (STTD), transmit Coherent Combining (CC) and Selection Diversity (SD) to distributed diversity systems. In contrast to the classical single hop system, the antennas in the distributed systems belongs to distributed relays instead of being co-located at the transmitter. The distributed relay diversity methods considered in this paper: Relay CDD (RCDD), Relay Alamouti (i.e.STTD), Relay CC (RCC) and Relay SD (RSD) are compared to the traditional 1-hop system. Analytical expressions for the received Signal to Interference Noise Ratio (SINR) are derived and used in a dynamic multi-cell multi-user simulator. Results show considerable SINR gains for both Round Robin and Max-SINR schedulers. The SINR gains translate into substantial cell throughput gains, up to 200%, compared to 1-hop systems. Despite its low complexity, the RCDD scheme has similar performance to that of other more sophisticated 2-hop schemes such as Relay Alamouti and Relay Coherent Combining. Marginally better results are observed for the Relay Selection Diversity scheme.
文摘In orthogonal frequency division multiplexing(OFDM)system,the time variation of a wireless channel destroys orthogonality among the sub-carriers,and this induces inter-carriers interference(ICI)and degrades system performance severely in mobile environment.In this paper,a new method of ICI cancellation based on delay diversity(DD)was proposed,which provides a way to mitigate the negative effect from the time variation of the wireless paths,thus improve the system performance greatly.The new method was called time-domain selfinterference cancellation(TDSIC)algorithm,which is different from other existing methods,such as frequencydomain method.In a cyclically extended OFDM system,the fading characteristics of extended OFDM symbols with different cyclic delay are different with each other,so in our TDSIC method,a new diversity collection scheme at the receiver end is proposed,which can be used to improve the system performance by suppressing ICI through selecting appropriate parameters.Moreover,the cyclically extended OFDM symbol at the transmitter side and diversity collection with different delay added OFDM symbols at the receiver side are used in the TDSIC method with the tradeoff of time-expense,so the well-known fixed delay for symbol at the transmitter side may be detected by the receiver side through estimating several parameters of wireless channels.In summary,the key of the TDSIC method is to improve the system performance with the cost of time.Based on performance analysis,simulation has proved that TDSIC may effectively improve the performance of the time-variant wireless channel.
