|Title of Invention||
A SYSTEM AND METHOD FOR SELECTING ANTENNAS IN A SATELLITE COMMUNICATION SYSTEM
|Abstract||A system and method for selectirlg and combining satellite communication signals from mtutiple antelmas. nle system includes at least. two signal paths (S50A,550B), each coupled to a separate antenna (202A- 202N), and a combiner (430) for combining signals from the two paths for processing by a signal processor (216). At least one of the two paths (550A,550B) includes a signal delay unit (410A-410B). The signal processor (216) carl distinguish a signal received from a source on one of the antennas (20ZA-202N) from that sign.,i1 received from the source on the other antenna (based on a signal delay produced by t1le signal delay urut (410A,410B). Each signal pafu (550) il1cludes a variable attenuator (526) for selectively coupling eaC'J"\ sig11al path (550) to the signal processor (216). lbe signal processor (216) determme$ the quality of the sig"t\als received along the signal paths (550),. arld provides t1ata regarding signal quality to a control processor (220), which maniplllates the attenuators to couple the signal path (550) having the highest qualIty signal to the sig.rlaJ processor (216).|
The present invention relates generally to satenne communication systems and more particularly to detecting and selecting satellite communication signals using multiple antennas.
thought ot as creating isolation using relative twenna anecuonary or sp division multiplexing. In addition, provided there is available bandwidth, each of these subdivisions, either sectors or beams, can be channelized. One way to channelize these subdivisions is to assign multiple CDMA channels through the use of frequency division multiplexing (FDM). In satellite systems, each CDMA channel is referred to as a "sub-beam," because there may be several of these per "beam."
In communication systems employing CDMA, separate links are used to transmit communication signals to and from a gateway or base station. A forward link refers to communication signals originating at the gateway or base station and transmitted to a system user. A reverse link refers to communication signals originating at a user terminal and transmitted to the cateway or base station.
In one type of spread-spectrum communication system, one or more preselected pseudo-noise (TN) code sequences are used to modulate or "spread" user information signals over a predetermined spectral band prior to modulation onto a carrier for transmission as communication signals. PN spreading, a method of spread-spectrum transmission that is well known in the art, produces a signal for transmission that has a bandwidth much greater than that of the date signal In the base station- or gateway-to-user terminal communication link, PN spreading codes or binary sequences are used to discriminate between signals transmitted by different base stations or over different beams. These codes are typically shared by all communication signals within a given cell or sub-beam.
A pair of pseudonoise (PN) code sequences can be used to modulate or "spread" information signals. Typically, one PN code sequence is used to modulate an in-phase (I) channel while the other PN code sequence is used to modulate a quadrature-phase (0) channel. This PN modulation or encoding occurs before the information signals are modulated by a carrier signal and transmitted as communication signals. The PN spreading codes are also referred to as short PN codes because they are relatively "short" when compared with other PN codes used by a communication system.
A common goal in the design of such multiple-access communications systems is to achieve the highest possible user capacity, that is, to enable the largest possible number of users to access the system simultaneously. System capacity can be limited by several factors, such as the number of user codes and CDMA channels available. However, spread spectrum systems are 'power limited", that is by the total amount of power allowed by all users to prevent unacceptable interference, and generally it is
the amount of power required to maintain forward link communications to system users that limits system capacity the most. If the amount of power required to maintain just a few of these links is large enough, the total power allocation is consumed well before the number of codes or frequencies available for more users are exhausted.
Therefore, it Is generally necessary to minimize the power required to "connect" each user or maintain their forward link in order to leave power for of her users and increase system capacity. This can be accomplished by increasing the ratio G/T of antenna gain G to receiver noise temperature T for each user. The higher this ratio or the antenna gain for each user, the logs; power required by that user for a link. When the gain of each user antenna is high then a sufficiently low amount of power is required to maintain the forward link and power is available for others.
In satellite communication systems, another design goal is to track or acquire and communicate with multiple satellites simultaneously One reason behind this goal is the desire to improve signal reception using signal diversify. Another reason is to accommodate communications with satellites which are in range, or in view, for relatively short periods of time, A common approach to achieving these goals is to optimize antenna design. One such design optimization is to utilize large, steerable, highly directional antennas. Another such design optimization is to combine the signals or multiple antennas to form a steerabie beam. One disadvantage of these approaches is that the manufacture and integration of such antennas is both complex and expensive.
Another such design optimization is to use multiple antennas, such as "patch" or helical antenna elements, that each cover a different sector of the sky. That is, each antenna has a radiation pattern that is optimized to covet a specific region of the sky or of a satellite constellation orbital pattern. This results in increased directivity and increased gain or G/T per antenna. A significant advantage of this approach is that less expensive antennas can be used. Unfortunately, the primary barrier to the use of multiple inexpensive antennas is the difficulty of detecting and selecting the appropriate signals from the antennas.
SUMMARY OF TOE INVENTION
The present invention is a system and method for detecting and selecting satellite communication signals from multiple antennas. In one embodiment, the system includes two signal paths, each coupled to a
distinguishing the signal received from the satellite by said first, second and third, or more, ones of the plurality of antennas based on said predetermined signal delays.
19. A system for selecting antennas based on received signal quality in a satellite communications -system having a satellite transmitting a signal and a user terminal having a plurality of antennas for receiving signals, comprising:
a first signal path coupled to a first one of the plurality of antennas;
a second signal path coupled to a second one of the plurality of antennas;
a first signal processor coupled to said first signal path;
a second signal processor coupled to said second signal path; and
a control processor, coupled to said first and second signal processors, that determines a relative quality of the signal on said first signal path and the signal on said second signal path and selects the one of the first and second ones of the plurality of antennas that receives the signal of higher quality.
20. The system of claim 19 further comprising at least a third signal path coupled to a third one of the plurality of antennas, and a third signal processor coupled to said third signal path and said control processor
21. A system for selecting antennas in a satellite communications system having a satellite transmitting a signal and a user terminal having a plurality of antennas substantially as herein described with reference to the accompanying drawings.
|Indian Patent Application Number||1024/MAS/1998|
|PG Journal Number||26/2007|
|Date of Filing||13-May-1998|
|Name of Patentee||QUALCOMM INCORPORATED|
|Applicant Address||6455 LUSK BOULEVARD, SAN DIEGO, CA 92121-1714.|
|PCT International Classification Number||H01R01/00|
|PCT International Application Number||N/A|
|PCT International Filing date|