Pulse or digital communications – Spread spectrum – Direct sequence
Reexamination Certificate
1998-08-17
2003-02-25
Le, Amanda T. (Department: 2634)
Pulse or digital communications
Spread spectrum
Direct sequence
C375S145000, C375S149000, C375S150000, C370S209000
Reexamination Certificate
active
06526091
ABSTRACT:
BACKGROUND
This invention relates generally to electrical telecommunication and more particularly to synchronizing transceivers of different users and even more particularly to methods and apparatus for synchronization based on orthogonal sequences having optimized correlation properties.
Modem communication systems, such as cellular and satellite radio systems, employ various modes of operation (analog, digital, and hybrids) and access techniques such as frequency division multiple access (FDMA), time division multiple access (TDMA), code division multiple access (CDMA), and hybrids of these techniques.
Digital cellular communication systems have expanded functionality for optimizing system capacity and supporting 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. 1
illustrates 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 contain an underlying microcell structure. The umbrella cell
10
includes microcell
20
represented by the area enclosed within the dotted line and microcell
30
represented by the area enclosed within the dashed line corresponding to areas along city streets, and picocells
40
,
50
, and
60
, which cover individual floors of a building. The intersection of the two city streets covered by the microcells
20
and
30
may be an area of dense traffic concentration, and thus might represent a hot spot.
FIG. 2
is a block diagram of an exemplary cellular mobile radiotelephone system, including an exemplary base station (BS)
110
and mobile station (MS)
120
. The BS includes a control and processing unit
130
which is connected to a mobile switching center (MSC)
140
which in turn is connected to the public switched telephone network (PSTN) (not shown). General aspects of such cellular radiotelephone systems are known in the art. The BS
1
110
handles a plurality of voice channels through a voice channel transceiver
150
, which is controlled by the control and processing unit
130
. Also, each BS includes a control channel transceiver
160
, which may be capable of handling more than one control channel. The control channel transceiver
160
is controlled by the control and processing unit
130
. The control channel transceiver
160
broadcasts control information over the control channel of the BS or cell to MSs locked to that control channel. It will be understood that the transceivers
150
and
160
can be implemented as a single device, like the voice and control transceiver
170
, for use with control and traffic channels that share the same radio carrier.
The MS
120
receives the information broadcast on a control channel at its voice and control channel transceiver
170
. Then, the processing unit
180
evaluates the received control channel information, which includes the characteristics of cells that are candidates for the MS to lock on to, and determines on which cell the MS should lock. Advantageously, the received control channel information not only includes absolute information concerning the cell with which it is associated, but also contains relative information concerning other cells proximate to the cell with which the control channel is associated, as described for example in U.S. Pat. No. 5,353,332 to Raith et al., entitled “Method and Apparatus for Communication Control in a Radiotelephone System”.
In North America, a digital cellular radiotelephone system using TDMA is called the digital advanced mobile phone service (D-AMPS), some of the characteristics of which are specified in the TIA/EIA/IS-136 standard published by the Telecommunications Industry Association and Electronic Industries Association (TIA/EIA). Another digital communication system using direct sequence CDMA (DS-CDMA) is specified by the TIA/EIA/IS-95 standard, and a frequency hopping CDMA communication system is specified by the EIA SP 3389 standard (PCS 1900). The PCS 1900 standard is an implementation of the GSM system, which is common outside North America, that has been introduced for personal communication services (PCS) systems.
Several proposals for the next generation of digital cellular communication systems are currently under discussion in various standards setting organizations, which include the International Telecommunications Union (ITU), the European Telecommunications Standards Institute (ETSI), and Japan's Association of Radio Industries and Businesses (ARIB). Besides transmitting voice information, the next generation systems can be expected to carry packet data and to inter-operate with packet data networks that are also usually designed and based on industry-wide data standards such as the open system interface (OSI) model or the transmission control protocol/Internet protocol (TCP/IP) stack. These standards have been developed, whether formally or de facto, for many years, and the applications that use these protocols are readily available. The main objective of standards-based networks is to achieve interconnectivity with other networks. The Internet is today's most obvious example of such a standards-based packet data network in pursuit of this goal.
In most of these digital communication systems, communication channels are implemented by frequency modulating radio carrier signals, which have frequencies near 800 megahertz (MHz), 900 MHz, 1800 MHz, and 1900 MHz. In TDMA systems and even to varying extents in CDMA systems, each radio channel is divided into a series of time slots, each of which contains a block of information from a user. The time slots are grouped into successive frames that each have a predetermined duration, and successive frames may be grouped into a succession of what are usually called superframes. The kind of access technique (e.g., TDMA or CDMA) used by a communication system affects how user information is represented in the slots and frames, but current access techniques all use a slot/frame structure.
Time slots assigned to the same user, which may not be consecutive time slots on the radio carrier, may be considered a logical channel assigned to the user. During each time slot, a predetermined number of digital bits are transmitted according to the particular access technique (e.g., CDMA) used by the system. In addition to logical channels for voice or data traffic, cellular radio communication systems also provide logical channels for control messages, such as paging/access channels for call-setup messages exchanged by BSs and MSs and synchronization channels for broadcast messages used by MSs and other remote terminals for synchronizing their transceivers to the frame/slot/bit structures of the BSs. In general, the transmission bit rates of these different channels need not coincide and the lengths of the slots in the different channels need not be uniform. Moreover, third generation cellular communication systems being considered in Europe and Japan are asynchronous, meaning that the structure of one BS is not temporally related to the structure of another BS and that an MS does not know any of the structures in advance.
In such digital communication systems, a receiving terminal must find the timing reference of a transmitting terminal before any information transfer can take place. For a communication system using DS-CDMA, finding the timing reference correspon
Nyström Johan
Popovic Branislav
Le Amanda T.
Telefonaktiebolaget LM Ericsson
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