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  • 1.
    Ahsin, Tafzeel ur Rehman
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS.
    Cooperative Communications: Link Reliability and Power Efficiency2012Doktoravhandling, monografi (Annet vitenskapelig)
    Abstract [en]

    Demand for high data rates is increasing rapidly for the future wireless generations, due to the requirement ofubiquitous coverage for wireless broadband services. More base stations are needed to deliver these services, in order tocope with the increased capacity demand and inherent unreliable nature of wireless medium. However, this would directly correspond to high infrastructure costand energy consumption in cellular networks. Nowadays, high power consumption in the network is becoming a matter of concern for the operators,both from environmental and economic point of view.

    Cooperative communications, which is regarded as a virtual multi-input-multi-output (MIMO) channel, can be very efficient in combating fading multi-path channels and improve coverage with low complexity and cost. With its distributed structure, cooperativecommunications can also contribute to the energy efficiency of wireless systems and green radio communications of the future. Using networkcoding at the top of cooperative communication, utilizes the network resources more efficiently.

    Here we look at the case of large scale use of low cost relays as a way of making the links reliable, that directly corresponds to reductionin transmission power at the nodes. A lot of research work has focused on highlighting the gains achieved by using network codingin cooperative transmissions. However, there are certain areas that are not fully explored yet. For instance, the kind of detectionscheme used at the receiver and its impact on the link performance has not been addressed.The thesis looks at the performancecomparison of different detection schemes and also proposes how to group users at the relay to ensure mutual benefit for the cooperating users.Using constellation selection at the nodes, the augmented space formed at the receiver is exploited for making the links more reliable. Thenetwork and the channel coding schemes are represented as a single product code, that allows us to exploit the redundancy present in theseschemes efficiently and powerful coding schemes can also be designed to improve the link performance.

    Heterogeneous network deployments and adaptive power management has been used in order to reduce the overall energy consumption in acellular network. However, the distributed structure of nodes deployed in the network, is not exploited in this regard. Here we have highlightedthe significance of cooperative relaying schemes in reducing the overall energy consumption in a cellular network.  The role of differenttransmission and adaptive resource allocation strategies in downlink scenarios have been investigated in this regard.It has been observed that the adaptive relaying schemes can significantly reduce the total energy consumption as compared to the conventionalrelaying schemes. Moreover, network coding in these adaptive relaying schemes, helps in minimizing the energy consumption further.The balance between the number of base stations and the relays that minimizes the energy consumption, for each relaying scheme is also investigated.

  • 2.
    Ahsin, Tafzeel ur Rehman
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS.
    Link Reliability in Cooperative Relaying Using Network Coding2010Licentiatavhandling, monografi (Annet vitenskapelig)
    Abstract [en]

    Demand for high data rates is increasing rapidly for future wireless systems.This trend is due to the increase in the number of mobile subscribers that need bandwidth hungry multimedia applications anywhere, anytime. Fourth generation cellular systems like IMT-advanced are being developed to meet these requirements. The unreliable nature of the wireless medium is one of the main hinderance in providing high data rates. Cooperative communication in cellular networks is emerging as a new paradigm to deal with the channel impairments. User cooperation via fixed relays in cellular systems form multiple access relay channels (MARCs) and provide an effective and cost efficient solution to achieve spatial diversity gains. Network resources can be utilized efficiently by using network coding at cooperating nodes.

    A lot of research work has focused on highlighting the gains achieved by using network coding in MARCs. However, there are certain areas that are not fully explored yet. For instance, the kind of the detection scheme used at the base station receiver and its impact on the link performance has not been addressed. In most cases, the outage probability has been used as a performance measure of MARCs. However, it is well known that the outage probability gives information about the signal availability, but it does not give the complete picture about the reliability of the link and the achieved quality of service.

    This thesis work looks at the link performance, in terms of symbol error probability, of multiple access relay channels that employ network coding at the relay node. Different types of detection schemes are considered and their performance is compared under different link conditions. Analytical expressions for the average symbol error probability of the cooperating users are derived. Focusing on the uplink of cellular systems, certain rules are devised on how to group users at relay node to ensure mutual benefit for the cooperating users. As a way of improving the link performance of multiple access relay channels and their robustness, the thesis considers constellation selection for the different branches. This method takes advantage of the redundancy between the transmitted symbols created by network coding and the augmented signal space obtained at the base station receiver. The obtained results show that, with a proper selection of the constellation sets, the link performance of MARCs can be improved. The thesis further looks at the interaction between the channel coding schemes of the cooperating users and network coding. It is shown that joint channel-network coding in MARCs can be seen as a product code. This new representation provides considerable flexibility in selecting efficient decoding algorithms at the base station receiver and gives the possibility to use more powerful network coding schemes for MARCs.

  • 3.
    Ahsin, Tafzeel Ur Rehman
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS.
    Ben Slimane, Slimane
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS.
    Constellation Selection in Network Coded Distributive Antenna System2009Inngår i: GLOBECOM 2009 - 2009 IEEE Global Telecommunications Conference / [ed] Ulema M, IEEE , 2009, 342-346 s.Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Relays can improve wireless links by providing an extra path to the direct path which together form a virtual multiple antenna system. Network Coded-Distributive Antenna System (NC-DAS) and Plain-Distributive Antenna System (P-DAS) are examples of realizations of such scenario. Although the asymptotic diversity gain for both the schemes is comparable, the network coded scheme can further take advantage of the redundancy and the extra dimension provided by the relay link. This extra signal dimension can be very useful when multilevel modulation is employed as it gives the possibility for a better spread of the modulation signal points within the augmented signal space. This article presents a simple and effective Constellation Selection (CS) scheme for all the three links within the NC-DAS system. This selection procedure improves the bit error probability in both AWGN and Rayleigh fading channels. Two different detections schemes are considered in the paper. Joint detection where the both users are decoded simultaneously and detection with successive cancelation where the strongest user is detected first followed by cancelation and maximum ratio combining. Analytical expressions for the error probability supported by simulation results are presented. The obtained results show that constellation selection provides good performance gain as compared to the case of same constellation.

  • 4.
    Ahsin, Tafzeel Ur Rehman
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS.
    Ben Slimane, Slimane
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS. KTH, Skolan för informations- och kommunikationsteknik (ICT), Centra, KTH Center för Trådlösa System, Wireless@kth.
    Energy Efficiency using Cooperative Relaying2011Inngår i: 2011 IEEE 22nd International Symposium On Personal Indoor And Mobile Radio Communications (PIMRC), New York: IEEE , 2011, 1698-1702 s.Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The rising demand for the high data rates in the future cellular systems, is directly linked with the power consumption at the transmitting nodes. Due to the various economical and environmental factors, it is becoming difficult to maintain the current rate of power consumption per unit of data, for the upcoming generations of the cellular systems. This has shifted the focus of many researchers towards the energy efficiency aspect of the cellular systems and power consumption has become an important design parameter in the recent works. In this article, we propose the use of cooperative communications using low cost fixed relays, in order to reduce the energy consumption at the transmitting nodes for a given quality of service requirement. It has been investigated that, how different factors, such as cell radius, relay position, number of relays and target data rate effects the area energy consumption for the different relaying schemes. It has been shown that, the cooperative relaying schemes along with adaptive resource allocation provides minimum energy consumption along with the better coverage as compared to the non adaptive cooperative relaying schemes.

  • 5.
    Ahsin, Tafzeel ur Rehman
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS.
    Ben Slimane, Slimane
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS.
    Network coding based on product codes in cooperative relaying2010Inngår i: IEEE Wireless Communications and Networking Conference 2010, WCNC 2010, 2010Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Employing network coding at the relay in cooperative relay system can improve the system throughput. However, XOR based network coding does not provide a strong error correction capability that can be used at the base station (receiver) in decoding the information of the cooperating users. Instead a block code can be used to combine the received user packets at the relay station where only the extra redundancy of the block code are forwarded by the relay station. With this structure a better error correction capability is embedded to the network coding scheme providing a better help to the receiver when decoding the user information. Combining this network coding structure with the individual block codes of the users, an overall product code can be obtained which gives the possibility of generating more powerful overall codes and increases the correction capability of the decoding process at the receiver. The obtained results show that the proposed scheme outperforms the conventional XOR based network coding scheme and gives the possibility of combining more users in the cooperation process.

  • 6.
    Ahsin, Tafzeel ur Rehman
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS.
    Slimane, Ben
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS.
    Detection strategies in cooperative relaying with network coding2010Inngår i: IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC, 2010, 12-17 s.Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Network coding in cooperative relaying can improve the performance of both users and provide improved efficiency as compared to the conventional relaying. This paper considers different detection schemes for cooperative relaying with network coding. Analytical upper bounds on the bit error probability are derived and used to assess the performance of the different schemes. The obtained results show that simple and low complexity detectors can provide good performance, quite close to that of joint detection.

  • 7.
    Ahsin, Tafzeel Ur Rehman
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS. KTH, Skolan för informations- och kommunikationsteknik (ICT), Centra, KTH Center för Trådlösa System, Wireless@kth.
    Slimane, Ben
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS. KTH, Skolan för informations- och kommunikationsteknik (ICT), Centra, KTH Center för Trådlösa System, Wireless@kth.
    Energy efficient resource allocation and deployment strategies for wireless networks2012Inngår i: 2012 5th International Conference on New Technologies, Mobility and Security - Proceedings of NTMS 2012 Conference and Workshops, IEEE , 2012, 6208715- s.Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Future wireless systems are being designed for extremely high data rates and are directly contributing to the global energy consumption. This trend is undesirable not only due to the environmental concerns, but to cost as well since energy costs are becoming a significant part of the operating expenditures for the telecom operators. Recently, energy efficient wireless systems have become a new research paradigm. Cooperative communication has shown good potential in improving coverage, providing robust radio links, reducing infrastructure cost, and has the possibility to reduce the total system energy consumption. This paper looks at possible deployment strategies for wireless networks that can reduce the energy consumption. We look at the tradeoff between the number of relay nodes and the number of base stations and their implications on the total energy consumption of wireless networks. The obtained results show that adaptive resource allocation between the base station and the relay node is an efficient way of reducing the energy consumption of the system. Furthermore, this reduction in energy consumption increases with increasing the system target spectral efficiency.

  • 8. Manssour, J.
    et al.
    Ahsin, Tafzeel ur Rehman
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS, Radio Systems Laboratory (RS Lab).
    Slimane, Ben
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS, Radio Systems Laboratory (RS Lab). KTH, Skolan för informations- och kommunikationsteknik (ICT), Centra, KTH Center för Trådlösa System, Wireless@kth.
    Osseiran, A.
    Analysis and performance of network decoding strategies for cooperative network coding2013Inngår i: Physical Communication, ISSN 1874-4907, E-ISSN 1876-3219, Vol. 6, 48-61 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this work, we present two new low-complexity network decoding strategies for cooperative network coding in a multiple-access relay channel scenario. For these two strategies, Selection and Soft Combining and Majority Vote Network Decoding, along with the optimal joint network decoding, we derive expressions for bit error probability performance as a function of the signal-to-noise ratio (SNR) of the different Rayleigh fading links, and show the tightness of the derived bounds through simulation results. The two proposed schemes provide a similar bit error probability (BEP) performance compared to the optimal scheme, while having significantly lower complexity. Further, we study the effect of user pairing on the error performance by considering different SNRs on the user and relay links towards the destination. It is also shown that the error performance of the different schemes follows the same trend for a given user pairing strategy.

  • 9.
    ur Rehman Ahsin, Tafzeel
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS. KTH, Skolan för informations- och kommunikationsteknik (ICT), Centra, KTH Center för Trådlösa System, Wireless@kth.
    Ben Slimane, Slimane
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS.
    A Joint Channel-Network Coding Based on Product Codes for the Multiple-Access Relay Channel2012Inngår i: ISRN Communications and Networking, ISSN 2090-4355, E-ISSN 2090-4363, Vol. 2012, 1-13 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The multiple access relay channel with network coding has the potential to achieve diversity and improve coverage of wireless networks. Its network coding scheme provides an extra redundancy that can be used at the receiver to improve the performance of the cooperating users. This paper shows that the combination of channel coding and network coding, in the multiple access relay channel, can be seen as a product code with rows formed by the code-words of the individual channel codes of the users and columns formed by the network coding code-words. This new representation allows the use of any decoding algorithm of product codes at the receiver to decode the information data of the cooperating users. This decoding process is a complete joint channel-network decoding algorithm as it sees the combination of the two coding schemes as a single coding scheme. It also gives the possibility to use network coding schemes more powerful than conventional XOR-based network coding. The obtained results show that the proposed product-based network coding structure can improve the performance of themultiple-access relay channel without reducing its efficiency and allow a very flexible cooperation between the involved users.

  • 10.
    ur Rehman Ahsin, Tafzeel
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS.
    Ben Slimane, Slimane
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS. KTH, Skolan för informations- och kommunikationsteknik (ICT), Centra, KTH Center för Trådlösa System, Wireless@kth.
    Area energy consumption in cooperative decode and forward (DF) relaying scenarios2011Inngår i: European Wireless 2011, 2011, 393-400 s.Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Energy efficiency in cellular networks has become an important design parameter in recent research works due to the global climate change and growing demand for very high data rates in future cellular systems. In our work, the main objective is to reduce the area energy consumption in a cellular network, for a given average spectral efficiency, in order to realize the green radio transmissions. The energy consumption for different transmission schemes such as direct link, decode and forward (DF) relaying with and without network coding is compared in this regard using a linear power consumption model. The impact of different parameters such as cell radius, the number and position of deployed relays and target spectral efficiency is studied for each transmission scheme. It has been concluded that DF relaying in general, provides moderate power savings as compared to the direct link transmission. Moreover, for a given outage probability, the network coding at the relay extends the cell coverage and provides higher spectral efficiency as compared to the conventional DF relaying and the direct transmission.

  • 11.
    Xu, Jie
    et al.
    University of Science and Technology of China.
    Qiu, Ling
    University of Science and Technology of China.
    ur Rehman Ahsin, Tafzeel
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS.
    Ben Slimane, Slimane
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS.
    Scheduling, Pairing and Ordering in the Network Coded Uplink Multiuser MIMO Relay Channels2010Inngår i: 2010 IEEE 71ST VEHICULAR TECHNOLOGY CONFERENCE, 2010Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Network coded multiuser uplink MIMO channels have been discussed in this paper. A three slots transmission is considered here and spatial division multiple access (SDMA) has been employed to serve multiuser simultaneously. Minimum mean-square-error successive interference cancellation (MMSE-SIC) is applied in the first two slots and singular value decomposition (SVD) is applied for the third slots. In order to get the optimal performance, user scheduling, decoding ordering and user pairing need to be considered. However, the optimal exhaust searching algorithm is too complex to implement. We propose a low complexity scheme to solve this problem and the simulation results show the performance gain. The proposed scheme is promising in the real systems.

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