Multiplex communications – Communication over free space – Combining or distributing information via code word channels...
Reexamination Certificate
1998-03-16
2001-01-16
Cangialosi, Salvatore (Department: 2732)
Multiplex communications
Communication over free space
Combining or distributing information via code word channels...
C370S320000
Reexamination Certificate
active
06175560
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates in general to telecommunications systems and more particularly to an apparatus and method of establishing and maintaining communication paths in a wireless telecommunications system.
BACKGROUND OF THE INVENTION
Wireless telecommunications systems require transmitters and receivers in order to send and receive information over radio frequency signals in a network configuration. These transmitters and receivers may suffer from interference with other transmitters and receivers in and out of the network configuration. Such interference may be caused by each transmitter operating at a different transmitting power level. Control of the transmitting power of the transmitters has only been performed at each transmitter and not from a centralized location. Further, the transmitting power of a transmitter within a wireless telecommunication system has proved to be difficult to control with respect to the transmitting powers of other transmitters in the system. Therefore, it is desirable to obtain improved control of the transmitting power of each transmitter within a wireless telecommunications system.
Also, wireless telecommunications systems require radio links be established between corresponding transmitters and receivers in order to provide wireless communication transmissions. Interference and delays occur in achieving acquisition and establishment of each radio link. It becomes inefficient to acquire and establish a radio link every time a call is to be initiated. Problems with interference also occur if a radio link is maintained whether or not a call is in progress due to power needed to maintain the radio link. Therefore, it is desirable to avoid establishing a radio link for each call and avoid inserting interference into the wireless telecommunications system through continuous maintenance of a radio link.
Additionally, transmitters typically transmit signals at one phase and receivers typically receive signals at a different phase. The different phases used by transmitters and receivers in the system may cause problems in recognizing information from multiple transmitter and receiver pairs. Further, a receiver having one phase requires a greater amount of circuitry and software support to identify information from a corresponding transmitter operating at a different phase. Additionally, a phase difference between a receiver and transmitter may also be affected by changes in a path delay between the transmitter and the receiver. Therefore, it is desirable to be able to control the phase of transmitters and receivers in a wireless telecommunications system to provide improved radio frequency signal transmission.
Transmitters of the originating or destination sources may send information at one phase and the receivers of the destination or originating sources may receive information out of phase. In such a situation, the receivers will not know at what portion in the data stream the receive process has started. Information is partitioned into frames and to adequately process the information the beginning of each frame should be identified. Conventional techniques to frame align information are cumbersome, slow in frame identification, and may lose frames of information. Therefore, it is desirable to quickly and easily identify the beginning of each frame of information to achieve proper processing.
SUMMARY OF THE INVENTION
U.S. Pat. No. 5,177,765 describes a technique for acquiring and tracking a direct sequence, spread-spectrum Time Division Multiple Access (TDMA) or Time Division Duplex (TDD) signal, in which techniques are used to align a receiver's Pseudo Random Sequence Generator (PRSG) with a transmitter's acquisition code transmitted within a particular time slot at the beginning of each frame.
U.S. Pat. No. 4,763,324 describes a method of frame decoding used in a signal transmission system having a frame structure. In order to improve the level of freedom from disturbances, the synchronising information is uniformly distributed over the bit flow.
Viewed from a first aspect, the present invention provides a method of establishing a downlink communication path in a wireless telecommunications system, comprising the steps of: receiving a downlink signal having a master code sequence including an orthogonal code, wherein the downlink signal is received in an acquisition mode at a first transmitting power and a first transmitting rate; adjusting a code and phase of a receiver slave code sequence in response to a code and phase of the master code sequence in order to recognise the downlink signal; searching for a frame alignment signal within the downlink signal; reading the downlink signal in response to finding two successive frame alignment signals; identifying a channel identifier signal within the downlink signal, the channel identifier signal identifying the orthogonal code included in the master code sequence; matching the channel identifier signal to a reference identifier code to verify that the correct downlink signal is being read; acquiring the downlink signal in response to a successful match.
Viewed from a second aspect, the present invention provides a central terminal for wireless communication with a plurality of subscriber terminals at fixed distances in a wireless telecommunications network, comprising: a transmit/receive unit operable to transmit a downlink signal having a master code sequence including an orthogonal code, and to receive an uplink signal having a slave code sequence, the downlink signal including a frame alignment signal to indicate a beginning of a frame of information, a code synchronization signal to adjust a transmitting rate of the uplink signal, a power control signal to adjust a transmitting power for the uplink signal, and a channel identifier signal identifying the orthogonal code included in the master code sequence, the channel identifier signal being useable by a subscriber terminal receiving the downlink signal to verify that that subscriber terminal is the correct subscriber terminal to receive the downlink signal, prior to a communication link with that subscriber terminal being established; an analogue card operable to perform analog to digital conversion of the received uplink signal and digital to analog conversion for the transmitted downlink signal;
a modem card operable to perform convolution coding and spreading functions on the downlink signal, the modem card operable to perform synchronization recovery, despreading, and error correction functions on the uplink signal;
a tributary unit operable to interface the modem card with a wireline telecommunication network for the transmission and reception of calls to and from the subscriber terminals;
a shelf controller operable to communicate control and data information with the analogue card, the modem card, and the tributary unit, the shelf controller acting as a bus master and the analogue card, modem card, and tributary unit acting as bus slaves, the shelf controller communicating control and data information in a first balanced protocol with an external network controller and communicating control and data information with the analogue card, modem card, and tributary unit in a second unbalanced protocol.
Viewed from a third aspect, the present invention provides a subscriber terminal for a wireless telecommunications system operating at a fixed distance from a central terminal, comprising: a receiver interface operable to receive a downlink signal in an unbalanced protocol from the central terminal, the downlink signal having a master code sequence including an orthogonal code, the receiver interface separating the downlink signal into I and Q signal components; a code generator and despreader operable to adjust a code and phase of a slave code sequence associated with the subscriber terminal in order to match a code and phase of the master code sequence of the downlink signal; a convolutional decoder operable to perform forward error correction on the I and Q signal components of the downlink
Bhagalia Shashikant
Cheung Yeung Joemanne Chi
Cooper Guy A.
Cooper Ian L.
Lysejko Martin
Airspan Networks Inc.
Baker & Botts L.L.P.
Cangialosi Salvatore
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