MIMO Capacity Research Articles

Improvement of MIMO System using STTC with Artificial Neural Network

The wide demand for high data rate rapid development in mobile and internet communication system limitation of the radio spectrum and the communication capacity needs cannot be met without a significant increase in communication spectral efficiency make it important to increase the capacity and decrease the Bit Error Rate (BER) of communication channel. In this paper, analysis of the capacity for four types of communication systems are performed, it was found that the MIMO communication system capacity is the best, Space Time Trellis Code (STTC) technique is used to improve the performance of MIMO system by decreasing the BER as well as possible, finally artificial neural network was used at the receiver of with (STTC) to get more suitable results by decreasing the BER of the proposed system.

Characterising an In-Room MIMO System Employing Elevation-Directional Access Point Antennas

The performance of an in-room MIMO system is investigated with the use of elevation-directional access point (AP) antennas which emphasize wall-reflected NLOS components instead of non-directional antennas. Simulation results suggest that the mean MIMO capacity throughout an idealised in-room environment can be improved on the order of 14% coupled with a 3% increase in mean relative MIMO gain if the appropriate main-lobe elevation direction is selected. The associated antennas are omnidirectional in azimuth and exhibit directivities and elevation half-power beamwidths on the order of 6 dBi and 28°, respectively. Experimental results obtained via channel measurements reveal more modest improvements due to the increased multipath richness exhibited by the real environment; a mean capacity improvement of approximately 5% is achieved, but this is accompanied by a minor reduction in relative MIMO gain. This level of performance may not be significant enough to warrant switching to elevation-directional AP antennas; however, the measured results provide qualitative verification of the simulation model. In any case, the results quantify the modest in-room MIMO performance gains one should expect when considering only wall reflections in the design of elevation-directional AP antennas at microwave frequencies.

Array of 8 Circularly Polarized Microstrip Antenna for 802.11ac MIMO WLAN

<p class="Abstract">An Array of 8 Circularly Polarizer Microstrip Antenna was proposed as MIMO antenna for IEEE 802.11ac MIMO WLAN system. The proposed antenna is applied for access point side. Antenna arrangement in two different polarization has investigated and the results show that setting the adjacent element with different polarization such as right hand and left hand circular polarization was used to suppress the mutual coupling between antenna. The highest mutual coupling is -26.8 dB. Each antenna element covers 480 MHz bandwidth. The calculation of estimated MIMO capacity that supported by the antenna shows that 1 Gbps capacity can be reach using the proposed antenna.<em></em></p>

PERFORMANCE ANALYSIS OF MIMO TECHNOLOGY USING VBLAST MAXIMUM A POSTERIORI (MAP)

Recent research shows that multiple antenna at both transmitter and receiver offers higher data rates compared to single antenna system. The information-theoretical capacity of MIMO grows linearly with the smaller of transmit and receive antenna in rich scattering environment with sufficient high SNR. In this paper, V-BLAST and maximum a-posteriori (MAP) is used improve the performance of the MIMO system. The original V-BLAST algorithm is a multi-layer symbol detection scheme, which detects symbols transmitted at different transmit antennas successively in a certain dataindependent order. The proposed V-BLAST-MAP algorithm differs from V-BLAST only in the ordering strategy of the symbols detected. The complexity of the V-BLAST-MAP is higher than that of V-BLAST. The performance improvement is also significant. In this paper, MATLAB Based simulation result are discussed .

Downlink User Capacity of Massive MIMO Under Pilot Contamination

Pilot contamination has been regarded as a main limiting factor of time division duplexing (TDD) massive multiple-input-multiple-output (Massive MIMO) systems, as it will make the signal-to-interference-plus-noise ratio (SINR) saturated. However, how pilot contamination will limit the user capacity of downlink Massive MIMO, i.e., the maximum number of users whose SINR targets can be achieved, has not been addressed. This paper provides an explicit expression of the Massive MIMO user capacity in the pilot-contaminated regime where the number of users is larger than the pilot sequence length. This capacity expression characterizes a region within which a set of SINR requirements can be jointly satisfied. The size of this region is fundamentally limited by the pilot sequence length. Furthermore, the scheme for achieving the user capacity, i.e., the uplink pilot training sequences and downlink power allocation, has been identified. Specifically, the generalized Welch bound equality sequences are exploited and it is shown that the power allocated to each user should be proportional to its SINR target. With this capacity-achieving scheme, the SINR requirement of each user can be satisfied and energy-efficient transmission is achieved in the large-antenna-size (LAS) regime. The comparison with two non-capacity-achieving schemes highlights the superiority of our proposed scheme in terms of achieving higher user capacity. Furthermore, for the practical scenario with a finite number of antennas, the actual antenna size required to achieve a significant percentage of the asymptotic performance has been analytically quantified.

MIMO Capacity for On-Body Communications in Scattered Environments

The reliability of on-body communications is a major requirement for many applications. This paper introduces a novel method to enable effective on-body communications, making use of several on-body antennas to create a virtual MIMO system. Strategies for the selection of the best wearable antenna placements based on appropriated metrics, with examples for a 2 × 2 MIMO system, are given. The model includes a statistical description of the antenna-user coupling, the channel variability due to body dynamics, as well as the scattered propagation environment. The channel model assumes that the received signal results from the contribution of one on-body component and of several environment multipath ones. The comparison in system performance between a street and inside an office shows that multipath in large environments is negligible compared to the on-body component (at the selected frequency of 2.45 GHz). The best performance is obtained when the sink (receiver) nodes are on the front and back of the body, and data sensors (transmitters) are on the head, with a relative capacity gain over SISO of roughly 2.

Effects of Mutual Coupling on LTE MIMO Capacity for Monopole Array: Comparing Reverberation Chamber Tests and Drive Tests

The roof of an automobile would appear to be an ideal platform to place multiple-input-multiple-output (MIMO) antennas, having a large ground plane with plenty of space to separate antennas for optimum embedded element radiation efficiency. However, styling concerns often require that the antennas are to be placed close together. Thus, mutual coupling plays an important role in the performance of an MIMO antenna system as it affects the embedded element efficiency and the channel correlation. In this letter, we present a comparison between the measured mutual coupling effect on the ergodic channel capacity of a 2 ×2 MIMO system in a reverberation chamber (i.e., Rayleigh channel) and in a suburban outdoor environment (i.e., Rician channel) at Long Term Evolution (LTE) radio band 13. The outdoor MIMO capacity was obtained during a vehicle drive test using commercial over-the-air (OTA) LTE test equipment. All measurements were conducted with two-element monopole antennas on a 24-in-diameter circular ground plane. The impact that mutual coupling has in the degradation of the embedded element radiation efficiency and increased correlation between the antennas, and ultimately the decrease in ergodic MIMO channel capacity, is highlighted by these measurements. In addition, the results provide insight into the differences of channel capacity obtained in the rich isotropic multipath environment of a reverberation chamber and the channel capacity obtained in a real-world suburban environment.

Study of the Colocated Dual-Polarized MIMO Capacity Composed of Dipole and Loop Antennas

The colocated dual-polarized dipole (DPD) and dual-polarized loop (DPL) MIMO channel performances are compared. Computation results show that, for the ideal electric and magnetic dipoles, the dual-polarized MIMO systems have identical channel capacity. But the contour plots of the capacity gain of the realistic DPD and DPL are different, due to the difference in antenna patterns. The cumulative distribution function (CDF) of the capacity gain in the two-mirror (TM) channel shows that, for small distance, the capacity gain obtained by the DPD is obviously smaller than that of the DPL, but, with the increase of the distance, the difference gets smaller. A DPL with low mutual coupling is fabricated. Measured results show that high MIMO capacities can be obtained by this DPL in both the anechoic chamber (AC) and the realistic office room. The capacity gain of the DPL antenna is 1.5–1.99, which basically coincides with the theoretical and numerical results. Furthermore, the capacity of the virtual DPL antenna with no mutual couplings is also investigated. It is shown that, in the AC, the mutual coupling will generally decrease the dual-polarized MIMO capacity; however, in the office room, the effect of mutual coupling is not always negative.

On the MIMO Capacity for Distributed System under Composite Rayleigh/Rician Fading and Shadowing

Wireless channels are commonly affected by short-term fading and long-term fading (shadowing). The shadowing effects must be taken into account also when mobility is present in the wireless scenario. Using a composite fading model, the total channel capacity can be studied for a scenario with short-term Rayleigh fading along with shadowing. This work provides quantitative results for these kinds of scenarios with Rayleigh fading and shadowing, considering also multiple-input and multiple-output systems, which have not been previously reported. In addition, the channel capacity has been studied in depth in its relation with the shadowing level, signal to noise ratio, and the number of elements in the multiple-input and multiple-output system. Moreover, the channel performance with shadowing has been compared to the one without it. Furthermore, Rician model with shadowing is studied and its results are reported. In addition, correlated and experimental results are provided. It is identified that the distributed MIMO systems can benefit from shadowing in Rician channels. This advantage has not been reported previously. This type of fading is proposed for massive MIMO by others and our results open the door to emulate massive MIMO on a reverberation chamber.

MIMO multiband antenna system with nonresonant elements

ABSTRACTMulti‐input multi‐output (MIMO) technology will enable high‐data rates in wireless devices to allow speech and video calls to streaming media and web browsing all over a common platform. MIMO technology needs M antennas both in transmission and reception. As the space in a wireless device is limited, including M antennas is a challenge. To face such challenge, a MIMO antenna system is proposed which comprises two small nonresonant elements operating in the frequency region 824–960 MHz and two identical elements operating at 1710–2170 MHz. The size of each of the nonresonant elements is only 5 × 5 × 5 mm3. The proposed MIMO system is analyzed in terms of bandwidth, efficiency, correlation, and multiplexing efficiency. MIMO capacity is measured in a reverberation chamber considering a free‐space Rayleigh scenario and also including the effect of a phantom head and hand. The results reveal that the proposed MIMO system provides capacity close to the ideal bound while having a small size and able to operate at several 2G, 3G, and 4G long term evolution standards. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:183–190, 2015

Ergodic Capacity of Nonlinear MIMO–OFDM Relaying Channels

This paper derives the ergodic capacity of nonlinear MIMO---OFDM relaying communication channels. We consider MIMO---OFDM relaying system where the transmitter, relays, and the receiver are all equipped with $$N_t$$Nt transmitting and $$N_r$$Nr receiving antennas, and the high-power amplifiers (HPAs) at the transmitter and relays exhibit general nonlinear behaviors. We derive closed-form expressions for the ergodic capacity of the system for both the amplify-and-forward (AF) and decode-and-forward (DF) relaying protocols. Our results show that AF relaying incurs higher capacity loss due to HPA nonlinearity than the DF relaying. The results also indicate that high-order MIMO systems suffer more capacity loss due to HPA nonlinearity than low-order MIMO systems, and that more capacity loss are experienced in multihop relaying over nonlinear channels as more relay hops are involved. This analysis complements existing works in the literature, where the effects of HPA on the error rate performance of MIMO systems have been documented. It also helps to stress the need for highly linearized HPA when relaying methods of wireless transmissions are desired.

Practical Analysis of Impact of Transmitter Hardware Impairments for MIMO Channel Measurement

Multiple Input Multiple Output MIMO is one of the promising technologies for the high data rate wireless Communication and adapted in many wireless standards. MIMO Channel measurement is an essential process based on which the decoding of symbols, equalization and adaptive transmission can be implemented. Hence, real time measurement of MIMO channel response and characterization is important one. Many research works has been carried out in the area of MIMO channel estimation and measurements under the assumption of no hardware impairment. But the practical hardware suffer from hardware impairments like IQ gain imbalance, skew and phase noise. MIMO systems are very sensitive for the above impairments which degrades the achievable capacity of the MIMO system. This paper presents an experimental real time study of indoor MIMO capacity measurement incorporating the hardware impairments. Algorithms are written in LABVIEW and implemented in SDR platform of National Instrument 6.6 GHz vector signal generator PXIe 5673 and vector signal analyzer PXIe 5663.

On multiple‐input–multiple‐output performance for Terrestrial Trunked Radio systems

Measurements for outdoor multiple-input-multiple-output (MIMO) capacity assessment are generally technically complicated, time consuming and expensive activities and few results are therefore published in the literature. Terrestrial Trunked Radio (TETRA) systems suffer from poor capacity and could be significantly improved by MIMO technology. However, performing outdoor channel measurements in relevant environments is very difficult because of interference problems with operating systems. In this study, the authors propose an estimation of the MIMO capacity for TETRA systems, based on outdoor MIMO measurements carried out at 300 MHz.

Dual-Layer EBG-Based Miniaturized Multi-Element Antenna for MIMO Systems

A dual-layer electromagnetic band-gap (EBG) mushroom structure is proposed in this paper. Based on the concept of slow-wave propagation, this structure can reduce the size of multi-element microstrip patch antennas (MPAs) by 61%. While the mushroom inner layer aids in the antenna miniaturization, the more compact upper layer acts as a band-stop filter further reducing the mutual coupling between the miniaturized patch antenna elements, which is otherwise not possible for a single-layer EBG structure. Various 2- and 4-element miniaturized MPAs are proposed for 2.5-GHz band applications, with antenna elements closely spaced at 0.5λ and low mutual coupling levels in the range of -28 dB to -50 dB. Furthermore, the achievable multiple-input-multiple-output (MIMO) channel capacities of these miniaturized multi-antennas are analyzed using the Kronecker channel model and tested in various propagation scenarios like the anechoic chamber, reverberation chamber and indoor. It is observed that the miniaturized MPAs can provide significant gains in MIMO capacity in all the signal scattering environments and are close to the theoretical limit of i.i.d. Rayleigh fading.

Efficient Transmission Mode Selection Scheme for MIMO-based WLANs

While single-user spatial multiplexing multiple-input multiple-output (SU-MIMO) allows spatially multiplexed data streams to be transmitted to one node at a time, multi-user spatial multiplexing MIMO (MU-MIMO) enables the simultaneous transmission to multiple nodes. However, if the transmission time required to send packets to each node varies considerably, MU-MIMO may fail to utilize the available MIMO capacity to its full potential. The transmission time typically depends upon two factors: the link quality of the selected channel and the data length (packet size). To utilize the cumulative capacity of multiple channels in MIMO applications, the assignment of channels to each node should be controlled according to the measured channel quality or the transmission queue status of the node.A MAC protocol design that can switch between MU-MIMO and multiple SU-MIMO transmissions by considering the channel quality and queue status information prior to the actual data transmission (i.e., by exchanging control packets between transmitter and receiver pairs) could address such issues in a simple but in attractive way. In this study, we propose a new MAC protocol that is capable of performing such switching and thereby improve the system performance of very high throughput WLANs. The detailed performance analysis demonstrates that greater benefits can be obtained using the proposed scheme, as compared to conventional MU-MIMO transmission schemes.

Influence of Environment Richness on the Increase of MIMO Capacity With Number of Antennas

We study the capacity of MIMO systems with uniform linear arrays in complex media, as the number of antennas increases. The distance between adjacent antennas is kept constant. The transfer matrix describing the channel is expressed in terms of the antennas and the physical characteristics of the environment using direct scattering theory. We prove that the capacity increases logarithmically when the number of antennas in the system belongs to a large interval of intermediate values. We then take the case where the number of antennas is large and we study the effects on the capacity of adding a new scatterer. Using a city model with buildings of different sizes, randomly distributed in space, we show numerically that initially the capacity increases at a nearly linear rate as the number of antennas increases. After a certain threshold the capacity growth becomes logarithmic. We show that the number of antennas where this transition occurs increases as the number of buildings increases.

MIMO multiband antenna system combining resonant and nonresonant elements

AbstractMulti‐input and multi‐output (MIMO) technology will enable high‐data rates in wireless devices to allow speech and video calls to streaming media and web browsing all over a common platform. MIMO technology needs M antennas both in transmission and reception. Because the space in a wireless device is limited, including M antennas is a challenge. To face such challenge, a MIMO antenna system is proposed, which comprises a multiband monopole antenna (35 × 15 mm2) and two small nonresonant elements, each one operating in a particular frequency region: 824–960 and 1710–2170 MHz. The size of each of the nonresonant elements is only 5 × 5 × 5 mm3. The proposed MIMO system is analyzed in terms of bandwidth, efficiency, correlation, and multiplexing efficiency. MIMO capacity is measured in a reverberation chamber considering a free‐space Rayleigh scenario and also including the effect of a phantom‐head and hand. The results reveal that the proposed MIMO system provides capacity close to the ideal bound, whereas having a small size and able to operate at several 2G, 3G, and 4G (long‐term evolution) standards. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:1076–1084, 2014

Iterative Antenna Selection for Multi-Stream MIMO under a Holistic Power Model

The design of wireless communication systems under holistic power models has been being a hot topic in green communications. In this letter, we shall investigate the antenna selection in multi-stream MIMO with circuit power consumption. The difficulty lies in the fact that the optimal active antennas can only be selected by exhaustive search. To reduce the complexity, two iterative properties of MIMO capacity with antenna selection under a holistic power model are first derived in this letter. An efficient iterative antenna selection algorithm can then be obtained directly from these properties. This algorithm enjoys a low complexity, and can be applied to both the transmitter and receiver. Simulation results will verify that the proposed algorithm achieves the near-optimal performance compared to exhaustive search.

MIMO CAPACITY COMPARISONS OF THREE TYPES OF COLOCATED DUAL-POLARIZED LOOP ANTENNAS

The 2 × 2 multiple-input-multiple-output (MIMO) capacities of three types of colocated dual-polarized loop (DPL) antennas with different current distributions and isolations are investigated in the free space (FS) channel, the corridor with perfect electric conductor walls (PEC corridor) and the corridor with concrete walls (CON corridor), separately. Capacity results show strong dependences on both the structure and the position of the DPL antenna, in addition to the propagation conditions. For all the three propagation scenarios, the largest capacity can be reached is in the PEC corridor, employing the DPL antenna with a uniform current distribution and a high isolation. Specifically, for a 20 dB signal-to-noise ratio (SNR), the maximum dual-polarized MIMO capacity is 13.1 bps/Hz, which is 1.97 time of that obtained by the one-polarized loop. It is also noted that, the rich-multipath environment can increase the robustness of the DPL MIMO system and the difference of the MIMO capacity obtained by different antenna structures will get smaller with respect to that in the FS channel.

Experimental Evaluation of MIMO Capacity for Ultrawideband Body-Centric Wireless Propagation Channels

In this letter, the capacity of ultrawideband (UWB) multiple-input-multiple-output (MIMO) on-body channels is evaluated. Three on-body channels are investigated-namely, Chest-Waist, Wrist-Waist, and Ankle-Waist channels. The data transmission capacities of each channel are evaluated and presented using the two power allocations schemes - namely, equal power allocation and the waterfilling power allocation. Statistical analysis is performed on the MIMO channel data, and the Rician K-factors of the channels are analyzed. It is found that the waterfilling scheme outperforms the equal power scheme in terms of capacity for all three on-body channels, with an average improvement of 1.2 b/s/Hz for signal-to-noise ratio (SNR) less than 12 dB (percentage improvement of 187% at 0 dB and 100% at 8 dB). However, the performances of the two schemes become comparable as the SNR increases with less than 0.28 b/s/Hz difference (percentage improvement of 3.6%) at an SNR level of 20 dB.