Macrodiversity Scheme Research Articles

Macro diversity for mmWave cellular communications in indoor environment

For the ITU-R defined enhanced mobile broadband (eMBB) type of generic services, 5G systems will deploy mmWave communications in indoor environments and open area scenarios in outdoor environment. Besides very high path-losses and reduced diffraction propagation mechanism, communications at these frequencies are known to be vulnerable to blockage effects caused by different obstacles, including human body. Thus, in this paper we examine efficiency of macro diversity (MD) solution for coping with these deteriorating effects in mmWave systems. In order to avoid frequent switching among base stations (BSs), which are in the communication range of a mobile station (MS), while keeping the performance on the required level, we analyze the best decision criteria for selection of a proper link, based on known channel quality indicators (CQIs). Using ns-3 module for mmWave communications, we model downlink (DL) communication at 28 GHz in mixed-office scenario, with both self-blockage and dynamic blockage included. Different BS and blocker densities are modeled in three real-case scenarios, in terms of MS mobility. The obtained results have confirmed efficiency of MD schemes for improving performance of mmWave communication systems in indoor environment.

Analysis of macro diversity based on maximum ratio combining in long range ALOHA networks

In low power wide area networks, packets transmitted by a device are not addressed to a specific base station: any surrounding station can receive them. This opens the way to several macro diversity schemes. As opposed to independent decoding of packets received by each base station, we propose using maximum ratio combining (MRC) to improve system performance. We use stochastic geometry to analyze the packet loss probability when MRC is implemented for both pure and slotted Aloha and obtain a closed formula when the path loss exponent $$\gamma $$ is 4. However, the formula is valid when all base stations on an infinite plane participate in the MRC procedure, which gives the most optimistic evaluation. We developed simulations to get the performance when a finite number of receivers in the MRC is considered and focus on the case with only 2 receivers. We use a curve-fitting approach based on the simulation results to get a closed-form formula of the packet loss probability with 2 receivers. This curve-fitting approach is also applicable to other cases in which more receivers are leveraged by MRC. The formula is easy to use and accurate when $$\gamma \in \left[ 3.3, 4.5\right] $$ and the loss probability is greater than $$0.5\%$$ . For pure Aloha when advanced transmission techniques (e.g., interleaving, robust channel coding, etc.) are applied and when the capture ratio is 3 dB, the system capacity for a $$10\%$$ packet loss probability is increased by a factor greater than 1.26 compared to a simple scheme in which each base station independently decodes packets.

Optimum Design of Closed-loop Macro Diversity Scheme for Cooperative Base Stations

Optimum Design of Closed-loop Macro Diversity Scheme for Cooperative Base Stations

A Closed-Loop Macro Diversity Scheme in Cooperative Multi-Point Downlink Transmission Systems

In this paper, the joint optimization issue of the cooperative precoder design is investigated for the transmission from the cooperative multi-point system to one mobile terminal. Based on the mean squared error minimization criterion, the problem is established for the cooperative precoder design. Unfortunately, this problem cannot be solved due to the block diagonal structure of the whole precoding matrix resulting from the fact that there is no data exchange among multiple base stations. In order to tackle this difficulty, the original problem is converted into an equivalent problem by stacking all of the nonzero entries in the block diagonal matrix into a long column vector. With the equivalent problem, the optimum solution is obtained in a closed-form expression by using the Lagrangian multiplier method. Numerical simulations illustrate the effectiveness of the proposed scheme in terms of bit error rate and spectral efficiency.

Design and Analysis on Macro Diversity Scheme for Broadcast Services in Mobile Cellular Systems

Recently, broadcast services are introduced in cellular networks and macro diversity is an effective way to combat fading. In this paper, we propose a kind of distributed space-time block codes (STBCs) for macro diversity which is constructed from the total antennas of multiple cooperating base stations, and all the antennas form an equivalent multiple input multiple output (MIMO) system. This code is termed High-Dimension-Full-Rate-Quasi-Orthogonal STBC (HDFR-QOSTBC) which can be characterized as: (1) It can be applied with any number of transmit antennas especially when the number of transmit antennas is large; (2) The code is with full transmit rate of one; (3) The Maximum Likelihood (ML) decoding complexity of this code is controllable and limited to Nt/2-symbol-decodable for total Nt transmit antennas. Then, we completely analyze the structure of the equivalent channel for the kind of codes and reveal a property that the eigenvectors of the equivalent channel are constant and independent from the channel realization, and this characteristic can be exploited for a new transmission structure with single-symbol linear decoder. Furthermore, we analyze different macro diversity schemes and give a performance comparison. The simulation results show that the proposed scheme is practical for the broadcast systems with significant performance improvement comparing with soft-combination and cyclic delay diversity (CDD) methods.

Resource Allocation for QoS-Aware OFDMA Using Distributed Network Coordination

This paper considers resource allocation for downlink orthogonal frequency-division multiple access (OFDMA). We propose a subcarrier and power-allocation method that differentiates users per service type to fulfill the quality-of-service (QoS) requirements of each user. Network coordination improves the performance of users at the border of the cells and, thus, decreases the minimum sum power for users with guaranteed performance (GP). Best effort (BE) users are then scheduled to maximize their sum capacity. The proposed method only assumes causal coordination between base stations and can be seen as a generalized macro diversity scheme suited for distributed networks. Numerical results show that network coordination increases the ratio of satisfied GP users, as well as the average data rate of BE users.

On the K and KG fading channels

In this paper, the composite Rayleigh-Gamma and Nakagami-Gamma distributions are considered. Multipath short-term fading and long-term fading (shadowing) affect wireless channels. A composite fading model was proposed for the modeling of shadowed channels, which resulted in a closed form solution for the probability density function (pdf). These composite Rayleigh-Gamma and Nakagami-Gamma are well-known as the K-distribution and KG-distribution, and are applied to cases where both micro- and macro-diversity schemes are implemented to mitigate short-term fading and shadowing, respectively. Thus, the composite pdf model offers significant improvement over approaches, which use lognormal pdf for shadowing. The results demonstrate the simplicity and usefulness of the composite pdf in the performance analyses of shadowed fading channels.

Macro-Diversity Scheme for a Point-to-Multipoint Communication System by means of D-STBC Method in Fast Fading Environment

In recent years, the space-time block coding (STBC) method has attracted attention to provide transmission diversity in mobile communication systems. Although the STBC method is very effective in slow fading environments, its performance in fast fading environments has yet to be clearly verified. In this paper we propose a railway radio communication system using space-time coding in cooperation with two base stations. Here, we considered the differential STBC (D-STBC) method in railway communication system to overcome difficulties caused by the fast fading environment. We have compared the performance of STBC and D-STBC method where there is frequency offset between two base stations. Moreover, we have presented the simulation result of overall performance of the system including frequency offset and transmission time delay when operating D-STBC method. The overall evaluation on this paper shows that the D-STBC method is suitable for realizing highly reliable railway communication systems.

Multimedia Broadcast Multicast Service Performance and its Enhancements in WCDMA Networks

Multimedia Broadcast Multicast Service (MBMS) in Wideband Code Division Multiple Access (WCDMA) networks is used to transmit information from one source to vast amount of recipients. The MBMS technique eases the load of the network and therefore allows network to serve more subscribers. The very aim of this study is to evaluate the performance of Release 6 MBMS and its performance enhancements in WCDMA networks. Special attention will be focused on macro and receive diversity which are considered in addition to time diversity provided by long interleaving as enhancements on MBMS performance. 3GPP Release 6 specifications for MBMS introduce two macro diversity schemes: soft and selective combining. The effect of those combining scheme concepts together with and without receive diversity provided by multiple receive antennas are examined. Also, a concept closely related to the receive diversity called Rx-switching i.e., turning the another receive antenna off in good channel situations for power saving purposes is studied. The system level performance of MBMS point-to-multipoint (p-t-m) mode is evaluated with dynamic system level tool in which e.g., mobility of users and interactions of the radio resource management functionalities are explicitly taken into account. Our studies indicate that macro diversity brings significant gains to the MBMS performance. Receive diversity together with macro diversity schemes improves the performance even more and therefore enhances the cell throughput that MBMS can offer. Furthermore, based on the findings of this study it seems that 2Rx Rake receiver can operate with a single antenna significant amount of time without sacrificing desired coverage and thus provide clear power saving opportunities.

Analysis of microdiversity and dual channel macrodiversity in shadowed fading channels using a compound fading model

Wireless channels are affected by short-term fading and long-term fading (shadowing). A compound fading model was proposed for the modeling of shadowed fading channels which resulted in a closed form solution for the probability density function (pdf) of the signal-to-noise ratio (SNR). This model is applied to a case where both micro- and macro-diversity schemes are implemented to mitigate short-term fading and shadowing, respectively. Using the compound fading model, it is shown that the pdf of the signal-to-noise ratio after the implementation of maximal ratio combining (MRC) at the micro level and selection combining (SC) at the macro level can be expressed in analytical form. Even when branch correlation exists, the pdf still can be expressed in analytical form. Thus, the compound pdf model offers significant improvement over approaches which use lognormal pdf for shadowing. The performance of a coherent binary phase shift keying (BPSK) modem is evaluated using this approach. The results demonstrate the simplicity and usefulness of the compound pdf in the performance analyses of shadowed fading channels even when branch correlation exists at the base station or correlation exists between base stations.

Effect of microdiversity and correlated macrodiversity on outages in a cellular system

We focus on maximum ratio combining at each base station and switching between base stations (BSs) as a simple macrodiversity technique. We obtain analytical results for pointwise outage probabilities for systems using one or a combination of both techniques to cover a desired area, assuming a certain correlation model for the set of path losses of the links connecting a terminal to the receiving BSs. Pointwise outage probabilities are averaged over the entire region of interest to get an estimate of the outage in the desired region. A comparison of micro- and macrodiversity schemes in terms of the outage gives insights as to the tradeoff between the two forms of diversity in the design of a cellular system.

Macrodiversity power control in hierarchical CDMA cellular systems

Hierarchical code division multiple access (CDMA) cellular systems, consisting of macrocells with underlying microcells, are studied. We seek power control schemes which will allow both hierarchical layers to share the same spectrum. For the reverse link, hierarchical maximal ratio combining (HMRC) is applied where each mobile station (MSs) is received and coherently combined by base stations (BSs) in both layers. For the forward link, selective transmit diversity (STD) is applied where each BS provides multiple transmit paths for MSs to choose. We show that both HMRC and STD are effective in hierarchical CDMA architectures. We conclude that hierarchical architectures are a viable solution for improving CDMA cellular system capacity, and a significant performance gain can be achieved without assigning disjoint spectrum between the layers, by utilizing macrodiversity schemes such as HMRC and STD.

High reuse efficiency of radio resources in urban microcellular systems

A new microcell configuration scheme in urban areas is proposed in order to increase the reuse efficiency of radio resources. Multiple directional-beam antennas lined up along a street form a cigar-shaped cell. Antennas are located at intersection and are directed along the intersecting streets. Two antennas facing each other form a microzone and, therefore, a cigar-shaped cell consists of multiple microzones in a line. Each microzone is protected against cochannel interference from neighboring microzones by confinement of transmitted signals to a microzone using down-tilting of antenna beams. Therefore, a radio channel which is occupied in one microzone can be used in adjacent microzones. An increase in system capacity is achieved by the high reuse efficiency of radio resources. The proposed system increases system capacity up to 560% with a call blocking probability of 1% when compared with a conventional system. In addition, a macrodiversity scheme using two antennas in a microzone improves the call quality on the reverse link.

The multiply-detected macrodiversity scheme for wireless cellular systems

The multiply-detected macrodiversity (MDM) scheme is proposed for wireless cellular systems. As opposed to the traditional macrodiversity schemes, in which at any time a signal from only one base station is selected, in the MDM scheme there is no selection, but all the received signals are detected, and a maximum-likelihood decision algorithm is employed to maximize the probability of correct decision. We study the performance of the MDM scheme and compare it with the performance of the traditional selection-based macrodiversity schemes. Depending on the propagation parameters, our results show that through the use of the MDM scheme, significant improvement in the bit-error rate (BER) can be achieved. For instance, if the outage probability is defined as BER above 10/sup -4/ the outage is eliminated at least 45% of the time as compared with signal-to-interference (S/I) diversity, for a propagation attenuation exponent of 4.0 and shadowing standard deviation of 4.0 dB. Furthermore, as compared with the (S/I) diversity, the MDM scheme reduces, on the average, the BER at least two orders of magnitude throughout more than 60% of the cell area for a propagation attenuation exponent of 3.5, shadowing standard deviation of 4.0 dB and system loading of less than 50%.

Macrodiversity technique for improvement in BERin wireless systems

The authors analyse a novel macrodiversity scheme, the multiply-detected macrodiversity (MDM) scheme, which relies on post-detection combining, as opposed to the traditional macrodiversity techniques, which are selection-based. The average fraction of the cell area is evaluated with an improved bit error rate (BER) performance, average BER improvement, and improvement in the average outage probability, relative to three other selection-based macrodiversity schemes. As a point of reference, the average improvement in BER is always at least one order of magnitude throughout at least 25% of the cell area, when the probability of the co-channel interferer's presence is not >70%.