Abstract
In this paper, we investigate the interference alignment schemes for the downlink of a heterogeneous network (HetNet), where the macro base station (BS) can serve arbitrary number of macro users. Furthermore, the number of data streams for macro users and pico users can be different. Firstly, we propose a basic grouping method aided interference alignment (IA) scheme and derive the transmit and receiver beamforming matrices in a closed-form expression. Furthermore, for the case where the number of antennas at pico BS is equal to the number of antennas at each user, we propose an advanced generalized eigenvalue decomposition (GEVD) based grouping method aided IA scheme which can reduce the number of transmit antennas required at the pico BS compared to the basic grouping method aided IA scheme. Moreover, we also derive the maximum total achievable degrees of freedom (DoF) for each scheme. In addition, it can be proved that the maximum total achievable DoF of the GEVD based grouping method aided IA scheme is higher than or equal to that of the basic grouping method aided IA scheme for the same configuration.
Highlights
Recent years, wireless networks have experienced exponential growing and the demand such as high data-rate transmission, high power/spectral efficiency and high quality of service (QoS) are considered in wireless communications
generalized eigenvalue decomposition (GEVD) BASED GROUPING METHOD AIDED interference alignment (IA) SCHEME we propose an advanced GEVD based grouping method aided IA scheme for the system model described in Section II with the configuration of Nr = Nt = N, i.e., the number of the receive antennas Nr for each user is equal to the number of transmit antennas Nt for each pico base station (BS)
1) THE NUMBER OF MACRO USERS K2 IS EVEN Theorem 3: For the heterogeneous network (HetNet) that consists of one macrocell and two picocells, where the macro BS serves K2 macro users and K2 is an even number, the maximum total achievable degrees of freedom (DoF) for the GEVD based grouping method aided IA scheme is independent of K2 and can be expressed as follows, DoF = min{Mt, 2N }
Summary
Wireless networks have experienced exponential growing and the demand such as high data-rate transmission, high power/spectral efficiency and high quality of service (QoS) are considered in wireless communications. For a two-cell uplink MIMO network, one IA scheme was proposed where the interference signals from users on the other cell are aligned into a low dimensional interference subspace [10]. The partial IA scheme was proposed in the downlink MIMO HetNet, in which there exist one macrocell and two picocells and only one macro user can be served [20]. We formulate the transmit and receiver beamforming matrices for the pico users to remove the ITI imposed on the macro users and CTI between picocells, respectively. There are two different scenarios, i.e., the number of users served by the macro BS, K2, is even or odd
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