03-10-2012, 12:39 PM
Energy-efficient wireless communication
[attachment=35121]
ABSTRACT
In this chapter we present an energy-efficient highly adaptive network
interface architecture and a novel data link layer protocol for wireless
networks that provides Quality of Service (QoS) support for diverse traffic
types1. Due to the dynamic nature of wireless networks, adaptations in
bandwidth scheduling and error control are necessary to achieve energy
efficiency and an acceptable quality of service.
In our approach we apply adaptability through all layers of the protocol stack,
and provide feedback to the applications. In this way the applications can
adapt the data streams, and the network protocols can adapt the
communication parameters.
Introduction
As already observed before in the previous chapters, the energy consumption of portable
computers like PDAs and laptops is the limiting factor in the amount of functionality
that can be placed in these devices. More extensive and continuous use of wireless
network services will only aggravate this problem. However, even today, research is still
focused on performance and (low power) circuit design. There has been substantial
research in the hardware aspects of mobile communications energy-efficiency, such as
low-power electronics, power-down modes, and energy efficient modulation. However,
due to fundamental physical limitations, progress towards further energy-efficiency will
become mostly an architectural and software-level issue.
Service model
Traditional communication networks provide a single service model that delivers
packets on a best effort basis. The available bandwidth is shared by competing senders
on a per packet basis. As a consequence, the packets experience an unpredictable – and
possibly very long – delay in getting to their destination. For many traditional
applications this is not a real problem as long as the overall delays are not excessive.
Other applications, however, that e.g. transfer digitised voice, require a predictable
service model. Circuit switched networks can offer such a service with a fixed slot of
bandwidth allocated for use by a sender in each time period, and with equal delivery
time for each slot.
It is expected that the new generation of wireless networks will carry diverse types of
multimedia traffic. Multimedia services, like packet audio and video, and real-time
services, e.g. for process control, have strict communication constraints. Multimedia
services are typically sensitive to delay and jitter (variations in delay) and demand high
bandwidths, but may be prepared to tolerate some data loss [36]. For example, dropping
several pixels in a high-resolution image may not be noticeable. Even dropping one
frame now and then from a video sequence at 25 frames per second can be tolerated.
Hard-real-time applications usually have lower
Wireless system architecture
Wireless LANs can be classified as distributed (ad-hoc) or centralised systems.
Essentially, the existence or lack of fixed wired infrastructure differentiates them.
• In ad-hoc networks the infrastructure is build up of mobiles which establish wireless
links between them and build a network topology allowing multihop connectivity.
Its key characteristics are that there is no fixed infrastructure, and that there is
wireless multihop communication, dynamically set up and reconfigurable as
mobiles move around.
• Centralised systems consist of base stations and mobiles. Its key characteristics are
that there is some fixed wired infrastructure, which is always accessible through a
single hop wireless link. The base stations are connected to the fixed network and
support the communication of the mobiles in range of the base station’s radio.
Ad-hoc networks provide more flexibility than centralised systems. However, in ad-hoc
networks the data possibly has to pass multiple hops before it reaches its final
destination. This leads to a waste of bandwidth as well as an increased risk of data
corruption, and thus potentially higher energy consumption (due to the required error
control mechanism). Only if the source and destination mobile are in each others reach,
ad-hoc networking can be more efficient. However, the use of ad-hoc networks is
limited because in general there is not much mobile-to-mobile communication, and in
many situations a fixed network is still required.
Overview of the chapter
In this chapter we will consider an ATM based infrastructure network where a basestation
co-ordinates access to one or more channels for mobiles in its cell. The channels
can be individual frequencies in FDMA, time slots in TDMA, or orthogonal codes or
hopping patterns in case of spread-spectrum. Hybrid TDMA/CDMA schemes benefit
from both the capacity of TDMA schemes to handle high bit-rate packet-switched
services, and the flexibility of CDMA techniques that allow smooth coexistence of
different types of traffic [5]. In this chapter we will deal with three main aspects
involved with energy-efficient wireless communication: Medium Access Control (MAC)
design, error control, and network interface architecture.
Section 5.2 first presents the basics of wireless data link layer design issues are
discussed, i.e. the wireless link limitations, the basic wireless networking functions
needed, and introduces the concept of QoS renegotiations. Section 5.3 determines the
main sources of energy consumption on wireless interfaces, which provide us the main
principles of energy efficient MAC design. Then, Section 5.4 presents a short
introduction to ATM and the peculiarities when applied to a wireless system. Section 5.5
presents various error-control alternatives and their consequences on energy
consumption. Then, Section 5.6 describes the basic principles and mechanisms of the
network interface architecture, and a new MAC protocol E2MaC whose design is driven
by energy consumption, diverse traffic type support, and QoS support considerations.
Section 5.7 provides an evaluation of the performance of the E2MaC protocol. Related
work is presented in Section 5.8, and we will finish with some conclusions.
Wireless data link layer network design issues
The context in this section is data link-level communication protocols for wireless
networks that provide multimedia services to mobile users. As mentioned before,
portable devices have severe constraints on the size, the energy consumption, and the
communication bandwidth available, and are required to handle many classes of data
transfer over a limited bandwidth wireless connection, including delay sensitive, realtime
traffic such as speech and video. This combination of limited bandwidth, high error
rates, and delay-sensitive data requires tight integration of all subsystems in the device,
including aggressive optimisation of the protocols to suit the intended application. The
protocols must be robust in the presence of errors; they must be able to differentiate
between classes of data, giving each class the exact service it requires; and they must
have an implementation suitable for low-power portable electronic devices
[attachment=35121]
ABSTRACT
In this chapter we present an energy-efficient highly adaptive network
interface architecture and a novel data link layer protocol for wireless
networks that provides Quality of Service (QoS) support for diverse traffic
types1. Due to the dynamic nature of wireless networks, adaptations in
bandwidth scheduling and error control are necessary to achieve energy
efficiency and an acceptable quality of service.
In our approach we apply adaptability through all layers of the protocol stack,
and provide feedback to the applications. In this way the applications can
adapt the data streams, and the network protocols can adapt the
communication parameters.
Introduction
As already observed before in the previous chapters, the energy consumption of portable
computers like PDAs and laptops is the limiting factor in the amount of functionality
that can be placed in these devices. More extensive and continuous use of wireless
network services will only aggravate this problem. However, even today, research is still
focused on performance and (low power) circuit design. There has been substantial
research in the hardware aspects of mobile communications energy-efficiency, such as
low-power electronics, power-down modes, and energy efficient modulation. However,
due to fundamental physical limitations, progress towards further energy-efficiency will
become mostly an architectural and software-level issue.
Service model
Traditional communication networks provide a single service model that delivers
packets on a best effort basis. The available bandwidth is shared by competing senders
on a per packet basis. As a consequence, the packets experience an unpredictable – and
possibly very long – delay in getting to their destination. For many traditional
applications this is not a real problem as long as the overall delays are not excessive.
Other applications, however, that e.g. transfer digitised voice, require a predictable
service model. Circuit switched networks can offer such a service with a fixed slot of
bandwidth allocated for use by a sender in each time period, and with equal delivery
time for each slot.
It is expected that the new generation of wireless networks will carry diverse types of
multimedia traffic. Multimedia services, like packet audio and video, and real-time
services, e.g. for process control, have strict communication constraints. Multimedia
services are typically sensitive to delay and jitter (variations in delay) and demand high
bandwidths, but may be prepared to tolerate some data loss [36]. For example, dropping
several pixels in a high-resolution image may not be noticeable. Even dropping one
frame now and then from a video sequence at 25 frames per second can be tolerated.
Hard-real-time applications usually have lower
Wireless system architecture
Wireless LANs can be classified as distributed (ad-hoc) or centralised systems.
Essentially, the existence or lack of fixed wired infrastructure differentiates them.
• In ad-hoc networks the infrastructure is build up of mobiles which establish wireless
links between them and build a network topology allowing multihop connectivity.
Its key characteristics are that there is no fixed infrastructure, and that there is
wireless multihop communication, dynamically set up and reconfigurable as
mobiles move around.
• Centralised systems consist of base stations and mobiles. Its key characteristics are
that there is some fixed wired infrastructure, which is always accessible through a
single hop wireless link. The base stations are connected to the fixed network and
support the communication of the mobiles in range of the base station’s radio.
Ad-hoc networks provide more flexibility than centralised systems. However, in ad-hoc
networks the data possibly has to pass multiple hops before it reaches its final
destination. This leads to a waste of bandwidth as well as an increased risk of data
corruption, and thus potentially higher energy consumption (due to the required error
control mechanism). Only if the source and destination mobile are in each others reach,
ad-hoc networking can be more efficient. However, the use of ad-hoc networks is
limited because in general there is not much mobile-to-mobile communication, and in
many situations a fixed network is still required.
Overview of the chapter
In this chapter we will consider an ATM based infrastructure network where a basestation
co-ordinates access to one or more channels for mobiles in its cell. The channels
can be individual frequencies in FDMA, time slots in TDMA, or orthogonal codes or
hopping patterns in case of spread-spectrum. Hybrid TDMA/CDMA schemes benefit
from both the capacity of TDMA schemes to handle high bit-rate packet-switched
services, and the flexibility of CDMA techniques that allow smooth coexistence of
different types of traffic [5]. In this chapter we will deal with three main aspects
involved with energy-efficient wireless communication: Medium Access Control (MAC)
design, error control, and network interface architecture.
Section 5.2 first presents the basics of wireless data link layer design issues are
discussed, i.e. the wireless link limitations, the basic wireless networking functions
needed, and introduces the concept of QoS renegotiations. Section 5.3 determines the
main sources of energy consumption on wireless interfaces, which provide us the main
principles of energy efficient MAC design. Then, Section 5.4 presents a short
introduction to ATM and the peculiarities when applied to a wireless system. Section 5.5
presents various error-control alternatives and their consequences on energy
consumption. Then, Section 5.6 describes the basic principles and mechanisms of the
network interface architecture, and a new MAC protocol E2MaC whose design is driven
by energy consumption, diverse traffic type support, and QoS support considerations.
Section 5.7 provides an evaluation of the performance of the E2MaC protocol. Related
work is presented in Section 5.8, and we will finish with some conclusions.
Wireless data link layer network design issues
The context in this section is data link-level communication protocols for wireless
networks that provide multimedia services to mobile users. As mentioned before,
portable devices have severe constraints on the size, the energy consumption, and the
communication bandwidth available, and are required to handle many classes of data
transfer over a limited bandwidth wireless connection, including delay sensitive, realtime
traffic such as speech and video. This combination of limited bandwidth, high error
rates, and delay-sensitive data requires tight integration of all subsystems in the device,
including aggressive optimisation of the protocols to suit the intended application. The
protocols must be robust in the presence of errors; they must be able to differentiate
between classes of data, giving each class the exact service it requires; and they must
have an implementation suitable for low-power portable electronic devices