Abstract
Hybrid digital-analog precoding is a cost effective solution for transmitting over the large bandwidths and huge antenna arrays available in the millimeter wave frequency bands. In this work we focus on the transmission of wideband signals over hybrid precoders that utilize Time-Modulated Arrays in the analog domain. We consider analog precoders constructed with Single-Pole-Double-Throw switches which are both flexible and efficient. We pose two Orthogonal Frequency-Division Multiplexing symbol configurations to cope with the harmonic interference introduced by the Time-Modulated Array. One does not take advantage of the wireless channel frequency diversity and the other does. We optimize digital and analog precoders to maximize the achievable rate in both symbol configurations. Optimization takes into account the switching devices efficiency and the inherent losses of this antenna technique. Finally, we show the excellent performance obtained with the proposed approach, in terms of achievable rate, compared to that of conventional phased arrays.
Highlights
The use of millimeter wave frequency bands in future wireless communication systems is promising because of the large spectrum availability
To alleviate the huge costs and power consumption associated to massive Multiple-Input Multiple-Output (MIMO) arrays, hybrid digital-analog architectures are helpful because they reduce the number of Radio Frequency (RF) chains [2]
To cope with the Harmonic Interference (HI), we provide an adaptation of the Orthogonal FrequencyDivision Multiplexing (OFDM) modulation to preserve the data subcarriers from the HI
Summary
The use of millimeter wave (mmWave) frequency bands in future wireless communication systems is promising because of the large spectrum availability. TIME-VARIANT SPDT TMA ANALOG PRECODING Let us consider a point-to-point wireless link where a transmitter with M antennas sends a wideband OFDM modulated signal to a single-antenna receiver. [FAq]M,NRF is a M × NRF matrix containing the q-th harmonic Fourier series coefficients of all the analog precoder time modulating signals. The feasible set of analog precoders, FA0 ∈ F , is convex This feature is in contrast to TMA approaches performing a phase weighting of the antenna elements in, e.g. [19], [20], and allows us to formulate analog precoding design problems as convex problems This equation reveals that the TMA radiates the RF signal s(t) centered at ωc, and replicas at the harmonic frequencies ωc + qω0, q ∈ Z. WIDEBAND TRANSMISSION MODEL Let us consider the wideband transmission of data symbols using an OFDM modulation with Nc subcarriers
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