Reducing message congestion in a communication system

Details Reducing message congestion in a communication system Reducing message congestion in a communication system

1999-12-30

2003-07-15

Vincent, David (Department: 2661)

Multiplex communications

Data flow congestion prevention or control

Flow control of data transmission through a network

C370S329000, C370S341000, C370S342000, C370S441000, C455S450000, C455S455000

Reexamination Certificate

active

06594233

ABSTRACT:

BACKGROUND
Applicant's invention relates to electrical telecommunication, and more particularly to wireless communication systems, such as cellular and satellite radio systems, for various modes of operation (analog, digital, dual mode, etc.), and for access techniques such as frequency division multiple access (FDMA), time division multiple access (TDMA), code division multiple access (CDMA), and hybrid FDMA/TDMA/CDMA.
In a TDMA cellular radio telephone system, each radio channel is divided into a series of time slots, each of which contains a burst of information from a data source, e.g., a digitally encoded portion of a voice conversation or digital control information. The time slots are grouped into successive frames that each have a predetermined duration. Successive time slots assigned to the same user, which are usually not consecutive time slots on the radio carrier, constitute a logical channel assigned to the user. As described in more detail below, such logical channels are provided for communicating control signals and for voice and data signals.
It can be seen that a TDMA cellular system operates in a buffer-and-burst, or discontinuous-transmission, mode: each terminal transmits (and receives) only during its assigned time slots or frames. Therefore, portions of the terminal, or mobile station (MS), which may be battery-powered, can be switched off, or “sleep”, to save power during the time slots when it is neither transmitting nor receiving. During assigned slots, a MS awakes and monitors the control channel for paging messages addressed to it.
For example, when an ordinary telephone (land-line) subscriber calls a mobile subscriber, the call is directed from the public switched telephone network (PSTN) to a mobile switching center (MSC) that analyzes the dialed number. If the dialed number is validated, the MSC requests some or all of a number of radio base stations (BSs) to page the called MS by transmitting over their respective control channels page messages that contain information, such as a mobile identification number (MIN), that identifies the called MS.
Each idle MS receiving a paging message compares the received identifying information with its own stored information. The MS having the matching identifying information transmits a page response over the particular control channel to the BS, which forwards the page response to the MSC. Upon receiving the page response, the MSC selects a traffic channel available to the BS that received the page response, switches on a corresponding radio transceiver in that BS, and causes that BS to send a message via the control channel to the called MS that instructs the called MS to tune to the selected voice or traffic channel. A through-connection for the call is established once the MS has tuned to the selected traffic channel.
A fully digitized type of cellular network uses logical channels for communicating digital voice or data as well as control information. One such digital cellular standard is defined by the TIA/EIA-136 standard, which is promulgated by the Telecommunications Industry Association and the Electronic Industries Association and is being adopted rapidly throughout the world. A cellular network implementing the TIA/EIA-136 standard transmits control information over digital control channels (DCCHs). A forward or downlink (BS to MS) DCCH includes successive repetitions of an ordered sequence of logical channels that makes up what is called a superframe. Such networks are described in U.S. Pat. No. 5,604,744 to Andersson et al. for “Digital Control Channels Having Logical Channels for Multiple Access Radiocommunication”, which is incorporated in this application by reference.
FIG. 1
shows a general example of a forward DCCH configured as a succession of time slots
1
,
2
, . . . , N, . . . included in the consecutive time slots
1
,
2
, . . . sent on a carrier signal. The DCCH slots may be defined on a radio-frequency carrier signal such as that specified by TIA/EIA-136, and may consist, as seen in
FIG. 1
for example, of every n-th slot in a series of consecutive slots that can be organized in TDMA blocks and frames. Each slot may have a duration of 6.67 milliseconds (ms), which is also the duration of a traffic-channel slot according to the TIA/EIA-136 standard. As shown in
FIG. 1
, the DCCH slots may themselves be organized into superframes (SF), and a superframe according to the standard may include thirty-two DCCH slots and have a duration of 640 ms.
Each superframe typically includes an ordered sequence of a number of logical channels that carry different kinds of information. One or more DCCH slots may be allocated to each logical channel in the superframe. The downlink superframe depicted in
FIG. 1
includes at least three logical channels: a broadcast control channel (BCCH) that includes six successive DCCH slots for overhead messages; a paging channel (PCH) that includes one slot for paging messages; and an access response channel (ARCH) that includes one slot for channel assignment and other messages. Other channels may be included in the exemplary superframe of
FIG. 1
, such as additional PCHs or other channels. As described in more detail below, other organizations of channels in a superframe are possible.
The superframes of a forward DCCH are advantageously organized into hyperframes, with one arrangement being depicted by
FIG. 2
in accordance with the TIA/EIA-136 standard. Each hyperframe comprises two superframes, one of which is usually designated the primary superframe and the other of which is usually designated the secondary superframe. A complete hyperframe (hyperframe
0
) and a successive partial hyperframe (hyperframe
1
) are shown in FIG.
2
. Each superframe comprises time slots that are organized into the following logical channels: a fast BCCH (F-BCCH), an extended BCCH (E-BCCH), a short message service BCCH (S-BCCH), and a SPACH. The SPACH typically comprises a short message service channel (SMSCH), a plurality of PCHs, and an ARCH, although any combination of these can make up a given SPACH frame. As noted above, each superframe may also include slots for other logical channels.
According to the TIA/EIA-136 standard, each superframe includes a complete set of F-BCCH information, which is system-related information such as the structure of the DCCH that a MS uses for accessing and maintaining communication with the BSs. This is described in Section 5.1.1, for example, of TIA/EIA Pub. No. SP-4027-123-A (Nov. 20, 1998). Also, every PCH in a primary superframe is repeated in the corresponding secondary superframe. Each MS is hashed to a DCCH in a cell based on a number of parameters, including portions of its user group identity or permanent mobile station identity, the number of DCCHs in the cell, and the number of slots allocated to the DCCHs. This process is described in TIA/EIA Pub. No. SP-4027-121-A, Section 8.1 (Nov. 20, 1998), which is incorporated in this application by reference.
Besides supporting sleep modes for MSs, digital control and traffic channels facilitate optimization of system capacity and support hierarchical cell structures, i.e., structures of macrocells, microcells, picocells, etc. The term “macrocell” generally refers to a cell having a size comparable to the sizes of cells in a conventional cellular telephone system (e.g., a radius of at least about 1 kilometer), and the terms “microcell” and “picocell” generally refer to progressively smaller cells. For example, a microcell might cover a public indoor or outdoor area, e.g., a convention center or a busy street, and a picocell might cover an office corridor or a floor of a high-rise building. From a radio coverage perspective, macrocells, microcells, and picocells may be distinct from one another or may overlap one another to handle different traffic patterns or radio environments.
FIG. 3
is an exemplary hierarchical, or multi-layered, cellular system. An umbrella macrocell
10
represented by a hexagonal shape makes up an overlying cellular structure. Each umbrella cell may cont

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