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This paper investigates the performance of the W band millimeter wave (mmWave) backhaul network proposed by our EU TWEETHER project. We focus on the downlink transmission of the mmWave backhaul network, in which each of the hubs serves a cluster of base stations (BSs). In the considered backhaul network, available frequency resources are first allocated to the downlink links with the consideration of fairness issue. In order to mitigate interference in the mmWave backhaul network, each hub operates the proposed algorithm, namely cooperation and power adaptation (CPA). Our simulation results show that, the backhaul network with mmWave capabilities can achieve a significant better throughput performance than the sub-6 GHz ultra high frequency (UHF) backhaul network. Furthermore, our simulations also reveal that the proposed CPA algorithm can efficiently combat interference in the backhaul network.

Traditional microwave based cellular networks are facing more and more challenges due to the exponential growth of data traffic. Shifting the communication spectrum from traditional microwave to millimeter wave (mmWave) is widely recognized as one of the best attractive solutions to future wireless communication networks demanding high-volume capacity. Moreover, mmWave small cell networks have been thought of as a promising approach to boost the coverage and rate of future cellular networks [

Wireless backhaul network with mmWave capabilities can be a promising candidate for future wireless communication systems, due to its advantages of high capacity, energy efficient, low transmission delay and low cost, etc. Most of the work about mmWave communication in the literature mainly focuses on channel modeling [

Against this background, in this paper, we investigate the performance of the W band mmWave backhaul network proposed by our EU TWEETHER project [

The rest of the paper is organized as follows. Section 2 provides the system model and states the main assumptions. Section 3 describes the subband allocation method. Section 4 proposes the interference mitigation schemes. Section 5 demonstrates the performance results. Finally, Section 6 summarizes the conclusions.

Our project, namely EU TWEETHER, proposes novel W band mmWave based heterogeneous wireless networks with high data rate distribution, spectrum- and energy-efficiency. The conceptual structure of the proposed network is shown in

In this paper, we consider the downlink transmission of the mmWave backhaul network, which consists of

where

A mmWave communication link is assumed to be non-line-of-sight (NLoS) if the line segment joining the mmWave BS and the user is blocked by buildings.

Otherwise, the link is thought of as line-of-sight (LoS). In (2),

rier frequency at the mmWave frequency band, and d represents the distance of a link. Furthermore,

For the sake of theoretical study, we deploy the sectored antenna model to characterize the practical array patterns. Let us denote

In (3), we assume the beamwidth of an antenna, such as

In our mmWave backhaul network, each hub is able to transmit information to its serving BSs by using all spectrum of B Hz available in W band. Furthermore, we assume a hub communicates with its serving BSs based on orthogonal frequency division multiplexing (OFDM) employing M subbands. Hence, in the downlink transmission of the backhaul network, the achievable rate of a BS served by its hub on a subband can be written as

In (4),

hub j, hence, we have

subbands available in the network. In (4),

In (5),

In the considered mmWave backhaul network, each hub first needs to assign the available spectrum resource to the its serving BSs, in other word, each hub is required to allocate the M number of subbands available to its BSs. However, the transmissions in the network will suffer from the interference generated by their co-subband links. Therefore, after subband allocation, we operate the proposed interference mitigation algorithm for the links suffering strong interference in order to improve the network’s throughput performance. Let us now first discuss the subband allocation.

As mentioned in Section 2, a hub is assumed to employ all the available frequency bands to communicate with its serving BSs based on OFDM scheme. Therefore, hub j needs to allocate M subbands to its

In order to achieve the best trade-off between the performance and implementation complexity, each hub employs the greedy algorithm for subband allocation. In this paper, for simplicity and without loss of generality, the number of subbands available is larger than the number of BSs served by each hub, i.e.

where

where

For the sake of improving throughput performance of our mmWave backhaul network, in this section we propose a novel interference mitigation scheme, namely cooperation and power adaptation (CPA).

After the subband allocation discussed in Section 3, a desired communication link may suffer from strong interference imposed by other links using the same subband. Hence, the CPA algorithm is operated for the poor links, which either experience strong interference from their co-subband links, or generating strong interference to their co-subband links. Let us denote the set of the poor backhaul communication links on subband m as

where

where

The proposed CPA algorithm utilizes BS cooperation to mitigate interference in the backhaul network, in which the space time block coding (STBC) aided cooperative transmission can be established for the poor links. When the cooperation for the transmission to BS n is set up by hub j and hub q, the SINR in (8) for the link becomes

Known from (13), the achievable data rate of BS n can be significantly improved when the interference

where

Based on the optimization problem in (14), the principles of our CPA algorithm can be given as follows.

In this section, we provide a range of simulation results for demonstrating the achievable performance including the outage probability and sum rate of our backhaul network with the aid of W band mmWave communication. Specifically, we also evaluate the performance of the proposed CPA algorithm in terms of mitigating interference in the network. For the sake of theoretical study, we assume that there are

In

Parameter | Value | Parameter | Value |
---|---|---|---|

1 GHz | −174 dBm/Hz | ||

94 GHz | 46 dBm | ||

10 dB | 10 dB | ||

−10 dB | −10 dB | ||

2.09 | 3.34 | ||

Std ( | 5.0 dB | Std ( | 7.6 dB |

mmWave backhaul network can significantly outperform the UHF network in all different minimum rate requirement scenarios. As shown, with the aid of the proposed CPA algorithm, the mmWave backhaul network can achieve a better outage probability performance, and a bigger performance gap can be observed in the range of

In

Finally,

requires higher implementation complexity and cost. Therefore, it is important to choose proper SIR and ICI thresholds by jointly considering the system requirement, implementation complexity as well as desirable performance. From

In this paper, we have investigated the performance of the W band mmWave backhaul network proposed by our EU TWEETHER project. In order to improve the network’s throughput performance, we have proposed the CPA algorithm to mitigate interference in the mmWave backhaul network. When the CPA algorithm is employed, the hubs are allowed to set up cooperative transmissions for the poor links, alternatively, the hubs are required to reduce the transmission power for some links that generate strong interference to other links. We have provided a range of simulation results including the outage probability and sum rate of the backhaul network. Our simulations have shown that, our mmWave backhaul network can significantly outperform the UHF backhaul network. Furthermore, our simulations have also implied that the proposed CPA algorithm can efficiently combat interference so that the backhaul network achieves a clear better performance. We conclude that the proposed CPA algorithm can be thought of as a promising solution for interference mitigation in our mmWave backhaul network.

This work is supported by EU H2020 TWEETHER project under grant agreement number 644678.

Shi, J., Ni, Q., Paoloni, C. and Magne, F. (2017) Efficient Interference Mitigation in mmWave Backhaul Network for High Data Rate 5G Wireless Communications. Int. J. Communications, Network and System Sciences, 10, 170-180. https://doi.org/10.4236/ijcns.2017.105B017