This paper proposes an improved hybrid beamforming system based on multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) system. The proposed beamforming system improves energy efficiency compared to the conventional hybrid beamforming system. Both sub-connected and full-connected structure are considered to apply the proposed algorithm. In the conventional hybrid beamforming, the usage of radio frequency (RF) chains and phase shifter (PS) gives high power and hardware complexity. In this paper, the phase over sampling (POS) with switches (SW) is used in hybrid beamforming system to improve the energy efficiency. The POS-SW structure samples the value of analog beamformer to make lower resolution than conventional system. The number of output data in POS is decided by the resolution of POS system. The limited number of POS decides the resolution of antenna array and the values of POSs are designed from maximum and minimum phase angle antenna array. Energy efficiency without the phase shifter is high although channel capacity is nearly similar with conventional system. Also, the amplifier with POS-SW system is proposed to improve the BER performance. According to the data bits, the output signals of POS are decided. The system with 2, 3 and 4 bits is simulated to prove the proposed algorithm. In order to overcome the loss of low-resolution system, the amplifier with POS-SW system using channel information is proposed. The average sum-rate of 4 bits system shows the similar performance with the conventional hybrid beamforming system. This structure can play an important role by increasing the energy efficiency of the wireless communication system that many antennas are used. It is shown that the BER, average sum rate and energy efficiency of the proposed scheme are more improved than the conventional hybrid beamforming system.
Millimeter wave (mmWave) in wireless communication is a key feature in the fifth generation (5G) communication [
In mmWave communication system, conventional hybrid beamforming requires a large number of high-resolution PSs to construct analog beamformers to solve high power consumption and hardware complexity [
The hybrid beamforming system has sub-connected or full-connected structure. In the sub-connected structure, each phase shifter is connected to each antenna array. On the other hand, in the full-connected structure, each phase shifter of RF chains is connected to one of antenna arrays. Also, the full-connected structure has higher hardware complexity and performance than sub-connected structure.
POS structure for hybrid beamforming system is proposed in [
In this paper, Section 2 shows the conventional hybrid beamforming system and Section 3 shows the proposed hybrid beamforming system with POS-SW. Section 4 shows the simulation results of proposed algorithm. Finally, Section 5 shows the conclusion of this paper.
The
where
where
where
And
where
The channel model of the beamforming system uses 3D channel model [
Although the perfect channel information cannot be acquired, the perfect channel information is assumed to show the maximum performance of the proposed algorithm. If the specific technique for the channel estimation is used, the performance can be degradation. The multi-user channel model is composed of single-user channels as follows,
The 3D channel of the
where
where
The energy efficiency (
where
To overcome hardware complexity of the conventional system, the POS-SW system is devised to reduce the resolution of the conventional hybrid beamforming system. The POS-SW is divided POS part and SW part in sub and full-connected structure.
The number of RF chains
where
Since each phase shifter in all RF chains is connected to one of antenna arrays in full-connected structure, the number of phase shifters,
where
Instead of the high-resolution PSs network in conventional beamforming system, each RF chain is connected to POS system which has output of
where the
The analog precoding matrix can be easily implemented by the parallel signals with
Bits | |
Sampling values ( |
---|---|---|
2 bits | 22 = 4 | |
3 bits | 23 = 8 | |
4 bits | 24 = 16 | |
2 |
A detailed description of the iterative scheme at the
Data: Channel
Result:
(1) for
(2) initialize
(3) While
(4)
(5)
(6) for
(7)
(8) end
(9)
(10)
(11) end
(12)
(13) end
(14)
(15) set
(16)
The energy efficiency of proposed algorithm is different from the conventional system. The energy efficiency
where the
This POS-SW based hybrid beamforming architecture has low hardware complexity and power consumption. First, the variable gain amplifier (VGA) is used to provide different gain compensation for phases of each analog precoding matrix, which is connected with a different number of antennas. Because the limited number of resolutions
The limited number of POS decides the resolution of antenna array and the values of POSs are designed from maximum and minimum phase angle antenna array. The proposed algorithm has high energy efficiency without phase shifter although channel capacity is nearly similar with conventional system.
The proposed POS-SW system has high energy efficiency with the loss of BER performance. The amplifier with POS-SW system is proposed to overcome the loss of performance.
The transmit signal with amplifier gain
where
The amplifier gain
The loss of BER exists in the low-resolutions system.
For evaluating the performance of the proposed algorithm, BER performances, average sum rate and energy efficiency are measured. The simulations in this proposed algorithm are performed in both sub-connected and full-connected structure of hybrid beamforming system. The simulation parameters in
Index | Parameter |
---|---|
Number of data streams | 4 |
Number of RF chains | 4 |
Number of transmit antennas | 16 |
Number of user devices | 4 |
Number of antennas in each device | 1 |
Number of subcarriers | 64 |
CP size | 16 |
Modulation order | QPSK |
Number of multi-paths | 7 |
The energy efficiency is improved when POS-SW systems with 2,3,4 bits are used. The similar performance is shown among the systems with three different bits. The high performance of energy efficiency gives advantage for designing the hybrid beamforming for wideband system. Specially, because of the frequency selectivity, path loss, delay spread, angle spread and the number of clusters, the large number of antenna array is required. The transmitter spends a lot of power consumption and cost in conventional system but the proposed POS-SW gives effective performance with high energy efficiency.
In this section, the simulation results of BER and average sum-rate are shown.
The conventional hybrid beamforming system with PSs network has high resolution which uses the channel information. However, the proposed algorithm applies the low resolution POS-SW system to make low hardware complexity. In POS-SW system, the analog precoding matrix
In
In this paper, the advanced precoding technique is proposed to improve the energy efficiency. Both sub-connected and full-connected structure are considered to apply the proposed algorithm. The POS-SW system is proposed with low resolution of analog beamformer in the hybrid precoding technique for improving energy efficiency. The proposed POS-SW algorithm gives low hardware complexity and power consumption in wideband wireless communication system. According to the data bits, the output signals of POS are decided. The POS systems with the 2, 3 and 4 bits are simulated to prove the proposed algorithm. In order to overcome the loss of low-resolution system, the amplifier with POS-SW system using channel information is proposed. The trade-off is shown in the BER and average sum-rate performance. Specially, the average sum-rate of the system with 4 bits shows the similar performance with the conventional hybrid beamforming system