32 research outputs found
Initial synchronisation of wideband and UWB direct sequence systems: single- and multiple-antenna aided solutions
This survey guides the reader through the open literature on the principle of initial synchronisation in single-antenna-assisted single- and multi-carrier Code Division Multiple Access (CDMA) as well as Direct Sequence-Ultra WideBand (DS-UWB) systems, with special emphasis on the DownLink (DL). There is a paucity of up-to-date surveys and review articles on initial synchronization solutions for MIMO-aided and cooperative systems - even though there is a plethora of papers on both MIMOs and on cooperative systems, which assume perfect synchronization. Hence this paper aims to ?ll the related gap in the literature
Multiple-Symbol Differential Sphere Detection Aided Successive Relaying in the Cooperative DS-CDMA Uplink
The conventional amplify-and-forward cooperative system is capable of achieving a superior performance with the aid of Multiple-Symbol Differential Sphere Detection (MSDSD), when compared to conventional differential detection (CDD) for transmission over time-selective channels. However, the conventional broadcast/cooperative twin-phase based relaying protocol encounters a 50% throughput loss imposed by half-duplex relaying. For combating this problem, in this paper, we create a MSDSD aided successive relaying based cooperative DS-CDMA system. We demonstrate that given the target BER of 10?4 , a diversity gain of up to 10 dB is achieved over the benchmark schemes employed without a throughput loss
Serial Search Based Code Acquisition in the Cooperative MIMO Aided DS-CDMA Downlink
Full text of this paper is not available in UHRAFocal blockade of postsynaptic acetylcholine receptors (AChRs) in a small region of the neuromuscular junction may cause long-term synapse elimination at that site. Blockade of the whole junction does not cause synapse loss, indicating that it is the contrast in postsynaptic activity between the blocked and unblocked regions which causes withdrawal of the synaptic terminals. This phenomenon can be explained by the dual role of calcium, both in controlling AChR gene transcription and influencing AChR aggregation. A computational model is provided and the stability of the solutions is confirmed by theoretical analysis and computer simulation
Initial Synchronisation in the Multiple-Input Multiple-Output Aided Single- and Multi-Carrier DS-CDMA as well as DS-UWB Downlink
In this thesis, we propose and investigate code acquisition schemes employing both colocated and cooperative Multiple Input/Multiple Output (MIMO) aided Single-Carrier (SC) and Multi-Carrier (MC) Code Division Multiple Access (CDMA) DownLink (DL) schemes. We study their characteristics and performance in terms of both Non-Coherent (NC) and Differentially Coherent (DC) MIMO scenarios. Furthermore, we also propose iterative code acquisition schemes for the Direct Sequence-Ultra WideBand (DS-UWB) DL. There is a paucity of code acquisition techniques designed for transmit diversity aided systems. Moreover, there are no in-depth studies representing the fundamental characteristics of code acquisition schemes employing both co-located and cooperative MIMOs. Hence we investigate both NC and DC code acquisition schemes in the co-located and cooperative MIMO aided SC and MC DS-CDMA DL, when communicating over spatially uncorrelated Rayleigh channels. The issues of NC initial and post-initial acquisition schemes as well as DC schemes are studied as a function of the number of co-located antennas by quantifying the attainable correct detection probability and mean acquisition time performances. The research of DS-UWB systems has recently attracted a significant interest in both the academic and industrial community. In the DS-UWB DL, initial acquisition is required for both coarse timing as well as code phase alignment. Both of these constitute a challenging problem owing to the extremely short chip-duration of UWB systems. This leads to a huge acquisition search space size, which is represented as the product of the number of legitimate code phases in the uncertainty region of the PN code and the number of legitimate signalling pulse positions. Therefore the benefits of the iterative code acquisition schemes are analysed in terms of the achievable correct detection probability and mean acquisition time performances. Hence we significantly reduce the search space size with the aid of a Tanner graph based Message Passing (MP) technique, which is combined with the employment of beneficially selected generator polynomials, multiple receive antennas and appropriately designed multiple-component decoders. Finally, we characterise a range of two-stage iterative acquisition schemes employing iterative MP designed for a multiple receive antenna assisted DS-UWB DL scenario
Non-coherent successive relaying and cooperation: principles, designs, and applications
Cooperative communication is capable of forming a virtual antenna array for each node (user) in a network by allowing the nodes (users) to relay the messages of others to the destination. Such a relay aided network may be viewed as a distributed multiple-input multiple-output (MIMO) system relying on the spatially distributed single antennas of the cooperating mobiles, which avoids the correlation of the antenna elements routinely encountered in conventional MIMO systems and hence attains the maximum achievable diversity gain. Therefore, the family of cooperative communication techniques may be regarded as a potential solution for future wireless networks. However, constrained by the half-duplex transmit/receive mode of most practical transceivers, the cooperative networks may impose a severe 50% throughput loss. As a remedy, successive relaying can be employed, which is capable of mimicking a full-duplex relay and thereby recovering much of the 50% throughput loss. Furthermore, for the sake of bypassing power-hungry and potentially excessive-complexity channel estimation, noncoherent detection techniques may be employed for multiple-antenna aided systems, because estimating all the associated channels may become unrealistic. Explicitly, the mobile-stations acting as relays cannot be realistically expected to estimate the source-to-relay channels. In order to motivate further research on noncoherent successive relaying aided systems, a comprehensive review of its basic concepts, fundamental principles, practical transceiver designs and open challenges is provide
Initial synchronisation in the multiple-input multiple-output aided single- and multi-carrier DS-CDMA as well as DS-UWB downlink
In this thesis, we propose and investigate code acquisition schemes employing both colocated and cooperative Multiple Input/Multiple Output (MIMO) aided Single-Carrier (SC) and Multi-Carrier (MC) Code Division Multiple Access (CDMA) DownLink (DL) schemes. We study their characteristics and performance in terms of both Non-Coherent (NC) and Differentially Coherent (DC) MIMO scenarios. Furthermore, we also propose iterative code acquisition schemes for the Direct Sequence-Ultra WideBand (DS-UWB) DL. There is a paucity of code acquisition techniques designed for transmit diversity aided systems. Moreover, there are no in-depth studies representing the fundamental characteristics of code acquisition schemes employing both co-located and cooperative MIMOs. Hence we investigate both NC and DC code acquisition schemes in the co-located and cooperative MIMO aided SC and MC DS-CDMA DL, when communicating over spatially uncorrelated Rayleigh channels. The issues of NC initial and post-initial acquisition schemes as well as DC schemes are studied as a function of the number of co-located antennas by quantifying the attainable correct detection probability and mean acquisition time performances. The research of DS-UWB systems has recently attracted a significant interest in both the academic and industrial community. In the DS-UWB DL, initial acquisition is required for both coarse timing as well as code phase alignment. Both of these constitute a challenging problem owing to the extremely short chip-duration of UWB systems. This leads to a huge acquisition search space size, which is represented as the product of the number of legitimate code phases in the uncertainty region of the PN code and the number of legitimate signalling pulse positions. Therefore the benefits of the iterative code acquisition schemes are analysed in terms of the achievable correct detection probability and mean acquisition time performances. Hence we significantly reduce the search space size with the aid of a Tanner graph based Message Passing (MP) technique, which is combined with the employment of beneficially selected generator polynomials, multiple receive antennas and appropriately designed multiple-component decoders. Finally, we characterise a range of two-stage iterative acquisition schemes employing iterative MP designed for a multiple receive antenna assisted DS-UWB DL scenario.EThOS - Electronic Theses Online ServiceGBUnited Kingdo
Towards an enhanced noncoherent massive MU-MIMO system
PhD ThesisMany multiple-input multiple-output (MIMO) downlink transmission schemes assume
channel state information (CSI) is available at the receiver/transmitter. In
practice, knowledge of CSI is often obtained by using pilot symbols transmitted
periodically. However, for some systems, due to high mobility and the cost of
channel training and estimation, CSI acquisition is not always feasible. The problem
becomes even more difficult when many antennas are used in the system and
the channel is changing very rapidly before training is completed. Moreover, as
the number of transmit/receive antennas grows large, the number of pilot symbols,
system overheads, latency, and power consumption will grow proportionately
and thereby the system becomes increasingly complex. As an alternative, a noncoherent
system may be used wherein the transmitter/receiver does not need any
knowledge of the CSI to perform precoding or detection. This thesis focuses on
the design of a noncoherent downlink transmission system to jointly improve the
performance and achieve a simple low complexity transmission scheme in three
MIMO system scenarios: low rate differential spacetime block coding (STBC) in a
downlink multiuser (MU-MIMO) system; high rate differential algebraic STBC in
a downlink MU-MIMO system; and differential downlink transmission in a massive
MU-MIMO system. Three novel design methods for each of these systems are
proposed and analysed thoroughly.
For the MIMO system with a low rate noncoherent scheme, a differential STBC
MU-MIMO system with a downlink transmission scheme is considered. Specifically,
downlink precoding combined with differential modulation (DM) is used
to shift the complexity from the receivers to the transmitter. The block diagonalization
(BD) precoding scheme is used to cancel co-channel interference (CCI) in
addition to exploiting its advantage of enhancing diversity. Since the BD scheme
requires channel knowledge at the transmitter, the downlink spreading technique
along with DM is also proposed, which does not require channel knowledge neither
at the transmitter nor at the receivers. The orthogonal spreading (OS) scheme is
employed to have similar principle as code division multiple access (CDMA) multiplexing
scheme in order to eliminate the interference between users. As a STBC
scheme, the Alamouti code is used that can be encoded/decoded using DM thereby
eliminating the need for channel knowledge at the receiver. The proposed schemes
yield low complexity transceivers while providing good performance.
For the MIMO system with a high rate noncoherent scheme, a differential STBC
MU-MIMO system that operates at a high data rate is considered. In particular,
a full-rate full-diversity downlink algebraic transmission scheme combined with a
differential STBC systems is proposed. To achieve this, perfect algebraic space
time codes and Cayley differential (CD) transforms are employed. Since CSI is
not needed at the differential receiver, differential schemes are ideal for multiuser
systems to shift the complexity from the receivers to the transmitter, thus simplifying
user equipment. Furthermore, OS matrices are employed at the transmitter to
separate the data streams of different users and enable simple single user decoding.
In the OS scheme, the transmitter does not require any knowledge of the CSI to
separate the data streams of multiple users; this results in a system which does not
need CSI at either end. With this system, to limit the number of possible codewords,
a sphere decoder (SD) is used to decode the signals at the receiving end.
The proposed scheme yields low complexity transceivers while providing full-rate
full-diversity system with good performance.
Lastly, a differential downlink transmission scheme is proposed for a massive MIMO
system without explicit channel estimation. In particular, a downlink precoding
technique combined with a differential encoding scheme is used to simplify the
overall system complexity. A novel precoder is designed which, with a large number
of transmit antennas, can effectively precancel the multiple access interference
(MAI) for each user, thus enhancing the system performance. Maximising the worst
case signal-to-interference-plus-noise ratio (SINR) is adopted to optimise the precoder
for the users in which full power space profile (PSP) knowledge is available to
the base station (BS). Also, two suboptimal solutions based on the matched and the
orthogonality approach of PSP are provided to separate the data streams of multiple
users. The decision feedback differential detection (DFDD) technique is employed
to further improve the performance.
In summary, the proposed methods eliminate MAI, enhance system performance,
and achieve a simple low complexity system. Moreover, transmission overheads
are significantly reduced, the proposed methods avoid explicit channel estimation
at both ends.King Fahad Security Collage at the Ministry of Interior - Saudi Arabia