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DH-HSM (Dual-Hop Hybrid Spatial Modulation)

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DH-HSM (Dual-Hop Hybrid Spatial Modulation) is a novel multiple-input multiple-output (MIMO) communication scheme that combines the benefits of spatial modulation (SM) and cooperative communication to enhance the transmission reliability and spectral efficiency of wireless communication systems. This technology is specifically designed for relay-assisted communication scenarios where the direct link between the source and destination is unreliable or weak.

SM is a MIMO technique that uses the multiple antennas at the transmitter to map a single data stream into a set of symbols, where each symbol is transmitted using a single antenna. In SM, only one active antenna is used for data transmission at a time, which reduces the complexity of the transmitter and receiver design. However, SM suffers from a limited number of active antennas, which limits its spectral efficiency. On the other hand, cooperative communication is a technique that uses an intermediate node, called a relay, to forward the data from the source to the destination. Cooperative communication enhances the transmission reliability and coverage area of wireless networks.

DH-HSM combines the benefits of SM and cooperative communication to enhance the spectral efficiency and transmission reliability of wireless networks. In DH-HSM, the transmission is divided into two hops. In the first hop, the source node transmits the data to the relay node using SM. In the second hop, the relay node transmits the data to the destination node using SM or a conventional MIMO technique. The selection of the transmission technique in the second hop depends on the channel conditions and the level of interference at the relay node.

DH-HSM has several advantages over the existing MIMO and cooperative communication techniques. First, DH-HSM enhances the spectral efficiency by using the available antennas at the source and relay nodes to transmit the data simultaneously. Second, DH-HSM enhances the transmission reliability by using the relay node to forward the data from the source to the destination. Third, DH-HSM reduces the complexity of the transmitter and receiver design by using only one active antenna at a time.

In the following sections, we will discuss the DH-HSM architecture, the signal model, the detection algorithm, and the performance evaluation.

DH-HSM Architecture:

The DH-HSM system consists of three nodes: the source node, the relay node, and the destination node. Each node is equipped with M antennas, where M > 1. The source node transmits the data to the relay node using SM, and the relay node forwards the data to the destination node using SM or a conventional MIMO technique. The selection of the transmission technique in the second hop depends on the channel conditions and the level of interference at the relay node.

Signal Model:

Let x be the data symbol that needs to be transmitted from the source node to the destination node. The data symbol x is a complex number that is drawn from a QAM constellation. Let s and r be the indices of the active antennas at the source and relay nodes, respectively. Let Hs and Hr be the channel matrices between the source and relay nodes, and the relay and destination nodes, respectively. The channel matrices Hs and Hr are MxM matrices, where M is the number of antennas at each node. The channel matrices Hs and Hr are assumed to be independent, identically distributed (i.i.d.), and follow a complex Gaussian distribution with zero mean and unit variance.

The transmitted signal from the source node to the relay node is given by:

y1 = Hsx + n1,

where n1 is the additive white Gaussian noise (AWGN) with zero mean and variance σ1^2.

The received signal at the relay node is given by:

y2 = HrHsx + n2,

where n2 is the AWGN with zero mean and variance σ2^2.

The transmitted signal from the relay node to the destination node is given by:

y3 = Hrx + n3,

where n3 is the AWGN with zero mean and variance σ3^2.

Detection Algorithm:

The detection algorithm in DH-HSM involves two stages: antenna selection and symbol detection.

Antenna Selection:

In the first stage, the relay node selects the active antennas for data transmission in the second hop. The selection of the active antennas depends on the channel conditions and the level of interference at the relay node. If the channel conditions between the relay and destination nodes are good, the relay node can use SM to transmit the data to the destination node. In this case, the relay node selects one active antenna for data transmission. If the channel conditions between the relay and destination nodes are poor, the relay node can use a conventional MIMO technique to transmit the data to the destination node. In this case, the relay node selects multiple active antennas for data transmission.

Symbol Detection:

In the second stage, the destination node detects the data symbol transmitted by the source node. The symbol detection involves two cases: single antenna transmission and multiple antenna transmission.

Single Antenna Transmission:

If the relay node uses SM to transmit the data to the destination node, the symbol detection involves the following steps:

  1. The destination node estimates the channel matrix Hr between the relay and destination nodes.
  2. The destination node calculates the correlation between the received signal y3 and the channel matrix Hr.
  3. The destination node selects the antenna index that maximizes the correlation.
  4. The destination node detects the data symbol x using the selected antenna index and the estimated channel matrix Hs between the source and relay nodes.

Multiple Antenna Transmission:

If the relay node uses a conventional MIMO technique to transmit the data to the destination node, the symbol detection involves the following steps:

  1. The destination node estimates the channel matrices Hr and Hs between the relay and destination nodes, and the source and relay nodes, respectively.
  2. The destination node calculates the correlation between the received signal y3 and the channel matrix Hr.
  3. The destination node detects the data symbol x using the estimated channel matrices Hs and Hr, and the received signal y2.

Performance Evaluation:

The performance of DH-HSM can be evaluated in terms of bit error rate (BER) and spectral efficiency. The BER is the percentage of bits that are received in error, and the spectral efficiency is the number of bits that can be transmitted per second per unit bandwidth.

Simulation results have shown that DH-HSM outperforms the existing MIMO and cooperative communication techniques in terms of BER and spectral efficiency. DH-HSM achieves a higher spectral efficiency by using the available antennas at the source and relay nodes to transmit the data simultaneously. DH-HSM also achieves a lower BER by using the relay node to forward the data from the source to the destination, which enhances the transmission reliability and coverage area of wireless networks.

Conclusion:

DH-HSM is a novel MIMO communication scheme that combines the benefits of SM and cooperative communication to enhance the transmission reliability and spectral efficiency of wireless networks. DH-HSM uses SM in the first hop and either SM or a conventional MIMO technique in the second hop, depending on the channel conditions and the level of interference at the relay node. DH-HSM achieves a higher spectral efficiency and a lower BER compared to the existing MIMO and cooperative communication techniques. DH-HSM is a promising technology for relay-assisted communication scenarios where the direct link between the source and destination is unreliable or weak.