3,213 research outputs found
Simultaneous Transmission and Reception: Algorithm, Design and System Level Performance
Full Duplex or Simultaneous transmission and reception (STR) in the same
frequency at the same time can potentially double the physical layer capacity.
However, high power transmit signal will appear at receive chain as echoes with
powers much higher than the desired received signal. Therefore, in order to
achieve the potential gain, it is imperative to cancel these echoes. As these
high power echoes can saturate low noise amplifier (LNA) and also digital
domain echo cancellation requires unrealistically high resolution
analog-to-digital converter (ADC), the echoes should be cancelled or suppressed
sufficiently before LNA. In this paper we present a closed-loop echo
cancellation technique which can be implemented purely in analogue domain. The
advantages of our method are multiple-fold: it is robust to phase noise, does
not require additional set of antennas, can be applied to wideband signals and
the performance is irrelevant to radio frequency (RF) impairments in transmit
chain. Next, we study a few protocols for STR systems in carrier sense multiple
access (CSMA) network and investigate MAC level throughput with realistic
assumptions in both single cell and multiple cells. We show that STR can reduce
hidden node problem in CSMA network and produce gains of up to 279% in maximum
throughput in such networks. Finally, we investigate the application of STR in
cellular systems and study two new unique interferences introduced to the
system due to STR, namely BS-BS interference and UE-UE interference. We show
that these two new interferences will hugely degrade system performance if not
treated appropriately. We propose novel methods to reduce both interferences
and investigate the performances in system level.Comment: 20 pages. This manuscript will appear in the IEEE Transactions on
Wireless Communication
Flat Cellular (UMTS) Networks
Traditionally, cellular systems have been built in a hierarchical manner: many specialized cellular access network elements that collectively form a hierarchical cellular system. When 2G and later 3G systems were designed there was a good reason to make system hierarchical: from a cost-perspective it was better to concentrate traffic and to share the cost of processing equipment over a large set of users while keeping the base stations relatively cheap. However, we believe the economic reasons for designing cellular systems in a hierarchical manner have disappeared: in fact, hierarchical architectures hinder future efficient deployments. In this paper, we argue for completely flat cellular wireless systems, which need just one type of specialized network element to provide radio access network (RAN) functionality, supplemented by standard IP-based network elements to form a cellular network. While the reason for building a cellular system in a hierarchical fashion has disappeared, there are other good reasons to make the system architecture flat: (1) as wireless transmission techniques evolve into hybrid ARQ systems, there is less need for a hierarchical cellular system to support spatial diversity; (2) we foresee that future cellular networks are part of the Internet, while hierarchical systems typically use interfaces between network elements that are specific to cellular standards or proprietary. At best such systems use IP as a transport medium, not as a core component; (3) a flat cellular system can be self scaling while a hierarchical system has inherent scaling issues; (4) moving all access technologies to the edge of the network enables ease of converging access technologies into a common packet core; and (5) using an IP common core makes the cellular network part of the Internet
Fundamental Limits of Caching in Wireless D2D Networks
We consider a wireless Device-to-Device (D2D) network where communication is
restricted to be single-hop. Users make arbitrary requests from a finite
library of files and have pre-cached information on their devices, subject to a
per-node storage capacity constraint. A similar problem has already been
considered in an ``infrastructure'' setting, where all users receive a common
multicast (coded) message from a single omniscient server (e.g., a base station
having all the files in the library) through a shared bottleneck link. In this
work, we consider a D2D ``infrastructure-less'' version of the problem. We
propose a caching strategy based on deterministic assignment of subpackets of
the library files, and a coded delivery strategy where the users send linearly
coded messages to each other in order to collectively satisfy their demands. We
also consider a random caching strategy, which is more suitable to a fully
decentralized implementation. Under certain conditions, both approaches can
achieve the information theoretic outer bound within a constant multiplicative
factor. In our previous work, we showed that a caching D2D wireless network
with one-hop communication, random caching, and uncoded delivery, achieves the
same throughput scaling law of the infrastructure-based coded multicasting
scheme, in the regime of large number of users and files in the library. This
shows that the spatial reuse gain of the D2D network is order-equivalent to the
coded multicasting gain of single base station transmission. It is therefore
natural to ask whether these two gains are cumulative, i.e.,if a D2D network
with both local communication (spatial reuse) and coded multicasting can
provide an improved scaling law. Somewhat counterintuitively, we show that
these gains do not cumulate (in terms of throughput scaling law).Comment: 45 pages, 5 figures, Submitted to IEEE Transactions on Information
Theory, This is the extended version of the conference (ITW) paper
arXiv:1304.585
A Novel Uplink Data Transmission Scheme For Small Packets In Massive MIMO System
Intelligent terminals often produce a large number of data packets of small
lengths. For these packets, it is inefficient to follow the conventional medium
access control (MAC) protocols because they lead to poor utilization of service
resources. We propose a novel multiple access scheme that targets massive
multiple-input multiple-output (MIMO) systems based on compressive sensing
(CS). We employ block precoding in the time domain to enable the simultaneous
transmissions of many users, which could be even more than the number of
receive antennas at the base station. We develop a block-sparse system model
and adopt the block orthogonal matching pursuit (BOMP) algorithm to recover the
transmitted signals. Conditions for data recovery guarantees are identified and
numerical results demonstrate that our scheme is efficient for uplink small
packet transmission.Comment: IEEE/CIC ICCC 2014 Symposium on Signal Processing for Communication
Multiple Access for Small Packets Based on Precoding and Sparsity-Aware Detection
Modern mobile terminals often produce a large number of small data packets.
For these packets, it is inefficient to follow the conventional medium access
control protocols because of poor utilization of service resources. We propose
a novel multiple access scheme that employs block-spreading based precoding at
the transmitters and sparsity-aware detection schemes at the base station. The
proposed scheme is well suited for the emerging massive multiple-input
multiple-output (MIMO) systems, as well as conventional cellular systems with a
small number of base-station antennas. The transmitters employ precoding in
time domain to enable the simultaneous transmissions of many users, which could
be even more than the number of receive antennas at the base station. The
system is modeled as a linear system of equations with block-sparse unknowns.
We first adopt the block orthogonal matching pursuit (BOMP) algorithm to
recover the transmitted signals. We then develop an improved algorithm, named
interference cancellation BOMP (ICBOMP), which takes advantage of error
correction and detection coding to perform perfect interference cancellation
during each iteration of BOMP algorithm. Conditions for guaranteed data
recovery are identified. The simulation results demonstrate that the proposed
scheme can accommodate more simultaneous transmissions than conventional
schemes in typical small-packet transmission scenarios.Comment: submitted to IEEE Transactions on Wireless Communication
Performance Studies of Multimedia Traffic in CDMA Cellular Network
The current generation of wireless cellular network is mostly used for voice
communication. Although data services such as short message services (SMS) are
available, voice communication still takes precedence. However, in the near
future, it is anticipated that wireless communication is expected to handle
multimedia traffic that is currently available on land networks. Multimedia traffic
includes video services such as real time video and audio, voice services and data
services similar to the ones available in the Internet. The cellular network carrying
multimedia traffic is analysed in a single cell where Code Division Multiple
Access (CDMA) protocol is used for users to access the network simultaneously.
The study is analysed for the reverse link communication, i. e., communication
between the user and the base station. CDMA is used because of its merits in
minimising the effect of interference, increasing cell capacity and high security
features compared to other access technologies. The model inputs include co-
channel interference, signal to noise ratio, bit error rate requirements, number of users, the channel access priority and threshold. Suitable assumptions to enable
simulation are made. The model is simulated to see the impact of complementing
data traffic along with voice and video traffic. The model is also simulated for
synchronous transmission and asynchronous transmission of packets. The results
shows that data traffic can be successfully complemented along with voice and
video traffic without significantly degrading voice and video delay. Data traffic
can tolerate delay but is loss sensitive. Data traffic delay can be used without
suffering any loss, even by reducing the data access priority. The model also
compared the effects of synchronous and asynchronous transmission.
Synchronous transmission indicated an overhead in packet delay compared to
asynchronous transmission. It is concluded from the work that voice, video and
data traffic can be served in a cell simultaneously with asynchronous transmission.
A higher bandwidth can assure a higher number of multimedia users in a
asynchronous CDMA cellular network. The model will serve as a useful design
tool
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