Pulse or digital communications – Spread spectrum – Direct sequence
Reexamination Certificate
2000-04-07
2001-11-13
Bocure, Tesfaldet (Department: 2631)
Pulse or digital communications
Spread spectrum
Direct sequence
C455S446000
Reexamination Certificate
active
06317453
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method and apparatus for configuring Pseudo-Random Noise offsets (“PN-offsets”) for a spread spectrum communications network and, more particularly, to a method and apparatus for minimizing PN-offset confusion.
BACKGROUND
Cellular communications systems technology has evolved commercially to the digital-based Code Division Multiple Access standard (“CDMA”). This standard has gradually gained acceptance over analog and narrow-band technologies because of superb characteristics in traffic capacity, voice quality, and security. For example, field tests under stressed conditions have verified CDMA predictions that cellular traffic capacities averaging fifteen times greater than analog systems are achievable.
CDMA is a “spread spectrum” technology. Information contained in a particular signal of interest is spread over a much greater bandwidth than the original signal. A CDMA cellular call starts with a standard rate of 9600 bits-per-second (“bps”). This is then spread to a transmitted rate of about 1.23 Megabits-per-second. The spread signal contains digital codes to associate the signal with users in a network cell. When the signal is received, the codes are removed from the desired signal, separating the users and returning the call to a rate of 9600 bps.
Spread spectrum communications have been traditionally used in military operations. Spread spectrum signals appear as a slight rise in the naturally occurring “white noise floor” or interference level. Accordingly, a spread spectrum signal is very difficult to jam, difficult to interfere with, and difficult to identify. In contrast, the signal power of the other transmission technologies is easier to detect and to intercept.
CDMA cellular networks are designed in conformance to the IS-95 standard established by the Telecommunications Industry Association (“TIA”). The IS-95 standard requires that the CDMA signal be Had by a Pseudo-Random noise, which is a random sequence of one and/or zero binary digits. The time duration of one binary digit is one chip. One chip is a 1,250 kHz or 0.813 micro-second segment. The IS-95 standard sets out a network Short Code chip length of 2
15
chips. The IS-95 standard also establishes a minimum phase “distance” between these sites as being sixty-four or 2
6
chips. This minimum “distance” is also referred to as a PILOT_INC constant for the network. Accordingly, the short code length of 2
15
is divided by the minimum PILOT_INC constant to establish that a maximum number of 2
9
or five-hundred and twelve PN-offsets are potentially available to a network.
Each CDMA network cell has a base transmission station (“BTS”). Each BTS distinguishes itself from other BTSs by transmitting a different phase of the CDMA Short Code at a given time. A “different phase” means a different time offset from the zero offset of the network system timing, measured in bitsper-second. This given time is the PN-offset or PN-phase for that BTS. To assure that the PN-offsets remain unique from each other, the BTSs remain synchronized to a common time reference provided by the Global Positioning System (“GPS”), a satellite-based navigation system.
Cell sites are deployed to accommodate cellular traffic density. Typically, traffic density is determined to be either dense-urban, urban, suburban, rural or highway. Dense-urban traffic is densest, and rural or highway traffic is the least dense. Coverage areas have the highest with low traffic density deploy large cells having cell radii typically attaining 15,000 meters. In comparison, coverage areas with high cellular traffic density deploy small cells having cell radii as small as 150 meters.
Conventionally, CDMA cellular networks are planned according to a predicted subscriber density population, which translates into the capacity-per-unit-area also known as Erlang units The cell radii are planned proportional to the predicted-Erlang capacity. But, cellular networks based on traffic predictions are unable to accommodate subscriber traffic density changes caused by, for example, new community developments, such as shopping mails or business districts. Once the antenna towers are built and the BTSs are installed, it is very difficult and time consuming to make significant changes in the CDMA cellular network design.
Further, the actual traffic density does not follow predicted cellular traffic patterns. Consequently, some network areas are over-designed with too much cellular coverage, while other areas are under-designed with too little coverage. Unpredictable “hot spots” and “cold spots” can occur at different locations of the network. Cells serving the hot spots are overloaded, but cells covering the cold spots are under-loaded. Further, an extraordinarily high traffic density can be generated in small areas at specific times, but not all the time. For example, traffic density increases that occur during rush hour periods, traffic jams, or stadium events.
With respect to cellular infrastructure, conventional construction technologies are expensive and require a large amount of time to establish A need exists in undeveloped nations with large populations that are without existing telecommunications infrastructures. The infrastructure costs can be prohibitive and the delay for services can be five years or longer.
Thus, a need exists for a method for initially configuring PN-offsets for a CDMA cellular network for insertion of small cells into a large cell network and for insertion of large cells into small-cell networks. Furthermore, a need exists for a method and apparatus for providing configurable cellular coverage for transient traffic-densities. Also, a need exists for a configurable cellular coverage that engages wireless backhaul services for rapid deployment in areas without a telecommunications infrastructure.
SUMMARY OF THE INVENTION
Thus provided herein is a method and apparatus for configuring a spread spectrum cellular network for small-cell inclusion.
A spread spectrum cellular network has a finite series of PN-offsets. To minimize PN-offset confusion, the finite series of PN-offets is portioned into a first and a second set. The second set is allotted to a large-cell reuse pattern. The first set is allotted for present or future small-cell reuse patterns. Separating the PN-offsets minimizes the occurrence of PN-offset confusion between the large cells and the small cells. With respect to the large cell reuse pattern, PN-offset confusion is further minimized by spacing further apart the PN-offsets of the second set.
In another aspect, the method for configuring the spread spectrum cellular network involves sectoring each cell of the plurality of cells into a plurality of sectors. The sectored cells are assigned PN-offsets that are adjacent in the finite PN-offset series. The adjacent PN-offsets are assigned together in each sector of the sectored cell while maintaining sufficient distance between cells that reuse an assigned PN-offset.
Also provided herein is a method of inserting a plurality of small cells into a spread spectrum cellular network, deploying a plurality of mobile small cells in a small-cell reuse pattern in the coverage hole, and transferring a plurality of cellular traffic to the deployed mobile small cells.
REFERENCES:
patent: 4901307 (1990-02-01), Gilhousen et al.
patent: 5193101 (1993-03-01), McDonald et al.
patent: 5504935 (1996-04-01), Vercauteren
patent: 5883889 (1999-03-01), Faruque
patent: 6049564 (2000-04-01), Chang Churui
Bocure Tesfaldet
Garlick Bruce
Nortel Networks Limited
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