Asymmetric internet access over fixed wireless access

Details Asymmetric internet access over fixed wireless access Asymmetric internet access over fixed wireless access

1998-03-31

2002-06-04

Hsu, Alpus H. (Department: 2662)

Multiplex communications

Communication over free space

Having a plurality of contiguous regions served by...

C370S345000, C370S350000, C370S458000, C370S524000, C455S450000

Reexamination Certificate

active

06400701

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to telecommunications networks and particularly, although not exclusively, to communicating packet data in Fixed Wireless Access (FWA) networks.
BACKGROUND TO THE INVENTION
In a fixed wireless access (FWA) telecommunications system, subscribers are connected to a backbone telecommunications network by means of radio links in place of traditional copper wires. Each of a plurality of subscribers is provided with a subscriber radio terminal. A plurality of subscriber radio terminals of a plurality of subscribers premises communicate with a base station which provides cellular coverage, typically in urban environments over a 5 km radius. Each base station may be connected to a Public Switched Telecommunications Network (PSTN) switch via a conventional transmission link, known as a backhaul link. A number of potential subscribers sites in a base stations' area of transmission can be of the order of several thousands. A single base station can serve up to several thousand subscribers, making the installation and maintenance cost of a fixed wireless access system lower than that of an equivalent copper wire access network.
Referring to
FIG. 1
herein, there is illustrated a prior art fixed wireless access system. A plurality of subscriber radio terminals
100
each comprising a transceiver
101
and an antenna
102
, part of a residential subscriber system (RSS) installed at a subscriber's premises, communicate with a radio base station
103
having a base station antenna
104
and a base station transceiver apparatus
105
. A plurality of such radio base stations
103
each communicate with a central office switch
106
to gain access to a backbone telecommunications network
111
, eg a Public Switched Telephone Network (PSTN) or an Integrated Services Digital Network (ISDN). In a geographical area, each base station
103
is connected to a local exchange switch
106
via a backhaul transmission line
107
which may comprise for example a terrestrial line eg fiber optic cable or coaxial cable, or a microwave transmission link. Communication between the subscriber radio terminal and the base station is via a wireless radio link
108
. Each local wireless link
108
between radio base station
103
and subscriber radio terminal
100
comprises an uplink beam from the subscriber transceiver and antenna to the radio base station, and a downlink beam transmitting from the radio base station antenna and transceiver to the subscriber antenna and transceiver. Equal spectrum of frequency slots are allocated for uplink and downlink according to a frequency division duplex scheme, in which a first frequency of a frequency pair is allocated for uplink transmission and a second frequency of the frequency pair is allocated for downlink transmission.
Conventional fixed wireless access systems are narrow band systems which are mainly designed for providing narrow band circuit switched telecommunications services such as telephony, fax or modem. On the other hand, with increased penetration of personal computers into domestic residential markets, access to Internet services is increasingly demanded by subscribers. Thus, it is desirable for subscribers to a FWA system to be able to connect their Personal Computers (PCs)
109
to their RSSs for accessing the Internet rather than require a conventional wire based communications network line to be installed at their premises. The most popular Internet services include world wide web services and downloading of files. In particular, subscribers are increasingly making use of Internet services downloaded from Internet service providers. Internet access traffic is characterized as being highly asymmetric in the transfer of data as between a subscriber and an Internet service provider. This results in a significant difference in data rate in one direction on a subscriber line compared with another, appropriate direction. Internet access also has the characteristic of having a relatively long holding time. For example, a World Wide Web (WWW) session may last for a few hours.
For example, a dominant Internet access traffic type in the residential subscriber market is generated by web browsing. Typical figures on an average download on a page of data by a subscriber is around 50 kBytes, and some estimates project an increase of this figure to around 150 kBytes by the year 2000. Assuming subscribers will tolerate a 6 second waiting time during the page download, a peak data rate for download of web browsing data over a fixed wireless access link is of the order of 64 kbits/s increasing to around 192 kbits/s by the year 2000. After page download, subscribers typically take time to study the information downloaded. Estimates of an average time for such study is around 24 seconds, giving an average data rate on a fixed wireless access downlink of around 13 kbits/s, estimated to increase to around 39 kbits/s by the year 2000.
However, on an uplink, data sent from a subscriber to an Internet service provider is typically very light compared to the data downloaded from the Internet service provider. An approximate estimate of uplink loading requirement is that the uplink loading is typically around one tenth of the downlink loading for Internet services, ie one subscriber will produce a peak uplink rate of around 6.4 kbits/s (increasing to 19.2 kbits/s by the year 2000) and an average data rate of 1.3 kbits/s (increasing to 3.9 kbits/s by the year 2000).
Whilst conventional fixed access wireless systems may be efficient for services, eg voice data, having a relatively balanced data rate in each direction, maintaining a circuit switched connection over a fixed wireless access link for services having an asymmetry of data rate as between different directions of a subscriber link is inefficient use of available wireless link bandwidth.
FIG. 2
of the accompanying drawings schematically illustrates a prior art uplink transmission from RSS antenna
102
to radio base station
103
. The uplink transmission
201
comprises a sequence of timeslots, each lasting approximately 300 microseconds. A first timeslot
202
of transmission
201
comprises an uplink transmission from subscriber to the base station. Timeslot
203
, immediately following timeslot
202
, would usually represent a pause in the transmission by the the subscriber whilst the base station receives data transmitted in timeslot
202
. Timeslot
204
, which immediately follows timeslot
203
, usually represents a gap when the RSS is still unable to make a downlink transmission to the subscriber RSS. Timeslot
205
, which immediately follows timeslot
204
, represents a second timeslot when the radio base station is able to make a downlink transmission to the subscriber RSS. Thus, each downlink transmission timeslot is separated by two intermediate timeslots.
Gap timeslot
204
represents a delay when the RSS may change the carrier frequency which it uses to transmit to the base station. Other procedures may also be executed by the RSS during timeslot
204
and other subscriber terminals may communicate with the base station. The gap may also exist in order to allow a transmit timeslot
205
(immediately following timeslot
204
) to be time aligned with other transmissions, ie to attempt to ensure that all transmissions to the radio base station arrive at the same time.
In addition to data transfer relating to internet services being asymmetric, ie, considerably more data being transmitted on the downlink than on the uplink as discussed herein above, the data transferred can be of a bursty nature, thus the data is transmitted intermittently, compared with, for example, voice data which tends to be continuous. The continuous nature of circuit switch data, such as voice, means that it is undesirable for the RSS to change the carrier frequency which results in gaps, such as timeslots
204
. However, for package switch data, the constraints of maintaining continuous data transfer is not present, therefore, it is more acceptable for the RSS to change car

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