Multiplex communications – Communication over free space – Combining or distributing information via time channels
Reexamination Certificate
1998-08-12
2002-06-25
Vincent, David (Department: 2661)
Multiplex communications
Communication over free space
Combining or distributing information via time channels
C370S474000
Reexamination Certificate
active
06411613
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to Time Division Multiple Access (TDMA) telecommunication systems and more particularly to a method of conveying information in such systems where the information is arranged in a new format.
2. Description of the Related Art
Wireless telecommunication systems use various schemes to allow multiple users to use (i.e., share simultaneously) a particular bandwidth. The bandwidth is part of or all of the band of frequencies allocated to the telecommunication system for conveying (i.e., transmitting and receiving) information. The information includes user information (e.g., voice) and signaling information. The signaling information are data generated by various equipment of the telecommunication system that are used by the telecommunication system to manage, process and convey the user information. One multiple access scheme that is widely used in many wireless telecommunication systems is called Time Division Multiple Access.
A TDMA wireless telecommunication system allows multiple users to use the same bandwidth by creating time frames (hereinafter “frames”) comprising time slots (hereinafter “slots”) within which each user is allowed to convey their information. Signaling information is also conveyed during each slot. Each slot or a group of slots are defined and are assigned to a particular user. Thus, each user is allowed to transmit and/or receive information in that user's assigned slot. In this manner, many users are able to use the same bandwidth thus increasing the user and/or information capacity of the system.
FIG. 1
depicts a typical scenario in a TDMA system where user
1
is conversing with user
2
. For the sake of clarity, only two users are shown. In an actual system, there is usually more than one base station and many more users throughout the system some of whom obtain access to base station
106
via a wireline telephony network such as the Public Switched Telephone Network (PSTN). The users have mobile equipment
100
and
112
(e.g., cellular phone) which they use to communicate with each other. Base station
106
represents part of the TDMA system's equipment which relays the user information in accordance with the signaling information and protocol used by the system. The protocol is a particular set of rules by which the system equipment and the user equipment initiate communication, convey information and terminate communication. Typically, protocols are established communication standards that are well defined and which are followed by many wireless telecommunication systems. Wireless communication channels
102
and
110
are commonly referred to as the uplink, which is the channel used by the users to transmit information to base station
106
. Communication channels
104
and
108
are commonly referred to as the downlink, which is the channel used by the users to receive information from base station
106
. The information (user and signaling) is conveyed over the uplink and downlink in the form of Radio Frequency (RF) signals.
FIG. 2
depicts a particular frame format and a slot format used by a protocol referred to as the IS-
136
standard. The IS-
136
standard is a protocol used by many TDMA wireless telecommunication systems in North America and South America. The frame format is the particular arrangement of the slots within frame
200
and the slot format the arrangement of user information and signaling information within each slot. In particular, frame
200
has a time duration of 40 milliseconds and is divided equally into six slots. IS-
136
allocates 30 KHz of bandwidth per carrier. The information rate (i.e., symbol rate) is 24.3 K symbols/sec. Each slot has a time duration of 6.67 milliseconds and comprises 324 bits. Although the frame format (i.e., six slots per frame) is the same for the uplink and the downlink, the slot formats are different. Slot
202
depicts the uplink slot format and slot
204
depicts the downlink slot format. Slots
202
and
204
each are divided into fields which are portions of the slot reserved for either user information or signaling information. For example, slot
204
has fields
206
and
208
labeled DATA each of which reserves 130 bits for user information. Field
210
of slot
204
has 28 bits reserved for signaling information referred to as SYNC. The significance of the different fields of signaling information of slots
202
and
204
is defined in the IS-
136
standard, TIA/EIA IS-
136
.
1
,
136
.
2
which is incorporated herein by reference.
Still referring to
FIG. 2
, for downlink slot
204
, the first 28 bits of information transmitted and received (i.e., conveyed) are the SYNC bits. The next 12 bits transmitted and received are signaling bits called Slow Associated Control Channel (SACCH) bits followed by 130 bits of DATA. The remainder of the information is transmitted in the order shown. The uplink information is transmitted and received in the order shown by slot
202
of FIG.
2
.
In IS-
136
, a maximum of either three (3) users or six (6) users are allowed to convey information within the frame and slot format discussed above. The number of users per frame depends on the mode at which the TDMA system is operating. In IS-
136
compliant systems there are two modes of operation. The first mode of operation is referred to as the Full Rate mode in which each user is assigned two slots per frame. The second mode of operation is called the Half Rate mode in which each user is assigned one slot per frame. Thus, there can be up to six users per frame in the Half Rate mode and up to three users per frame in the Full Rate mode or a combination of both modes can be used in one system.
FIG. 3
depicts a user allocation scheme used in IS-
136
Full Rate mode (Frame
300
) and Half Rate mode (Frame
302
) for the uplink and the downlink. In the Full Rate mode, user
1
is assigned to slots
1
and
4
, user
2
is assigned to slots
2
and
5
and user
3
is assigned to slots
3
and
6
. In the uplink and downlink slot formats, the SYNC fields are used to allow the user information (i.e., DATA) to align and synchronize a user's information to the proper slot. Thus, the SYNC fields assist the system to delineate the slots. Each SYNC field has a bit pattern unique to the slot within which it is located.
Prior to being transmitted over a wireless communication channel, the user and signaling information are processed to attenuate adverse effects on the information caused by channel noise and other channel distortions. In particular, the RF signals, which carry the user and signaling information, are exposed to various well known distorting effects such as phase jitter, frequency offset, amplitude and phase fading and multipath distortions.
TDMA signals, especially uplink signals, are by nature bursty signals; that is the signals for any particular user are transmitted and received as short intermittent bursts each of which carries a great deal of information. When a transmitted or a received burst of information is adversely affected by channel distortions, a great amount of the information is lost. Therefore, to reduce the likelihood of losing large amounts of information, a certain amount of processing of the information is done prior to transmission. The intent of the processing is twofold; first it is to introduce redundancy to the information with the use of well known channel coding techniques. Channel coding protects information from errors by selectively introducing redundancies in the conveyed information. The second intent of the processing is to add time diversity to the information by spreading out in time the burst of information using the well known technique of interleaving. Interleaving is used to obtain time diversity in a communication system. Since channel coding techniques are designed to protect against channel errors that occur randomly or in a bursty manner, interleavers scramble the time order of the information to achieve time diversity and improve the performance of th
Seymour James Paul
Tonello Andrea M.
Law Office of John Ligon
Lucent Technologies - Inc.
Vincent David
LandOfFree
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