Wireless direct sequence spread spectrum digital cellular telephone system

• US 5,570,349 A
• Filed: 06/07/1994
• Issued: 10/29/1996
• Est. Priority Date: 06/07/1994
• Status: Expired due to Term

• Current Assignee: Lctl Wireless Investment LLC (Intellectual Ventures LLC)
• Original Assignee: Stanford Telecommunications, Inc. (Nokia Corporation)
• Inventors: Bustamante, Herman, Magill, David T., Natali, Francis
• Primary Examiner(s): Hsu, Alpus H.
• Application Number:
  US08/257,324
• Time in Patent Office: 875 Days
• Field of Search: 370/13, 370/17, 370/18, 370/19, 370/21, 370/24, 370/29, 370/32, 370/98, 370/22, 375/200, 375/205, 375/206, 375/208, 375/327, 375/345, 375/346, 375/367, 375/371, 375/373, 379/57, 379/58, 379/59, 379/60, 379/61, 455/33.1, 455/33.2, 455/49.1, 455/50.1, 455/51.1, 455/52.1, 455/523, 455/53.1, 455/54.1, 455/56.1, 455/63, 455/65, 455/67.1, 455/67.3, 455/67.4, 455/67.6 , 455/68, 455/69, 455/70
• US Class Current: 370/335
• CPC Class Codes: H04B 7/10 Polarisation diversity; Directional diversity
• CPC Class Codes: H04B 7/216 Code division or spread-spectrum multiple access [CDMA, SSMA]
• CPC Class Codes: H04B 7/2628 using code-division multiple access [CDMA] or spread spectrum multiple access [SSMA] H04B7/2618 takes precedence
• CPC Class Codes: H04W 52/42 in systems with time, space, frequency or polarisation diversity
• CPC Class Codes: H04W 84/14 WLL [Wireless Local Loop]; RLL [Radio Local Loop]

Abstract

The present invention is based on novel implementation techniques which makes orthogonal CDMA practical in a short range mobile telephone environment where significant multipath fading exists. Specifically, this invention provides novel techniques for establishing the time base, frequency, and power control necessary to achieve orthogonality. Use of a high power sounding burst on the outbound link permits: 1) antenna diversity selection to minimize the probability of a faded condition, 2) local frequency locking at the subscriber terminal which avoids the requirement for a costly precision frequency standard, and 3) essentially instantaneous inbound power control based on the outbound receive signal level. This is effective since time division duplexing is used and both transmission and reception take place on the same frequency. With the short frame structure and unique placement of the sounding burst the correlation between the outbound and inbound path losses is very high. Thus, according to the invention, the signal structure and control algorithms result in a greatly reduced signal level range at the base station/PBX to achieve high efficiency in a orthogonal CDMA system. Real world effects such as filtering, multipath time spread, and time base error destroy orthogonality and introduce a degree of cross coupling between supposedly orthogonal channels. Thus, the invention provides accurately controlled power levels in this highly dynamic environment.

Claims

1. In a spread spectrum orthogonal code division multiple access (OCDMA) communication system having at least one base station and a plurality of user handsets in which a set of orthogonal Radamacher-Walsh (RW) function are overlaid with a pseudonoise (PN) sequence forming a coded spreading sequence for an information signal, each orthogonal function of said set carries voice data for a single user in said system, a source of selected carrier signals and means to modulate said information signal on said carrier signal to form a transmit signal with said coded spreading sequence on said transmit signal for radio broadcasting between said at least one base station and said user handsets, each said user handset having a time base and means for controlling its power transmission, and wherein the base station transmits a sounding signal, the method of controlling operation of said handsets, the improvement comprising:

(1) measuring the time base error of each handset at said base station and transmitting time base correction information from said base station to each handset and controlling the timing of operation of each handset thereby, respectively, and

(2) measuring the power of the sounding signal and performing the compensation of the handset transmit power using instantaneous power control of handset to base station link so as to avoid signal interference.

2. In a spread spectrum orthogonal code division multiple access (OCDMA) communication system having at least one base station and a plurality of user handsets in which a set of orthogonal Radamacher-Walsh (RW) functions are overlaid with a pseudonoise (PN) sequence forming a coded spreading sequence for an information signal, each orthogonal function of said set carries voice data for a single user in said system, a source of selected carrier signals and means to modulate said information signal on said carrier signal to form a transmit signal with said coded spreading sequence on said transmit signal for radio broadcasting between said at least one base station and said user handsets, each said user handset having a time base and means for controlling its power transmission, and wherein the base station transmits a sounding signal, the improved method of controlling operation of said handsets comprising:

(1) means for measuring the time base error of each handset at said base station and transmitting time base correction information from said base station to each handset, respectively,

(2) means for measuring the power of sounding signal and performing the corresponding compensation of the handset transmit power and means for using the measured power to each handset to instantaneously control transmitted power of handset to base station link so as to avoid signal interference.

3. In a spread spectrum orthogonal code division multiple access (OCDMA) communication system having at least one base station and a plurality of user handsets in which a set of orthogonal Radamacher-Walsh (RW) functions are overlaid with a pseudonoise (PN) sequence forming a coded spreading sequence for an information signal, each orthogonal function of said set carries voice data for a single user in said system, a source of selected carrier signals and means to modulate said information signal on said carrier signal to form a transmit signal with said coded spreading sequence on said transmit signal for radio broadcasting between said at least one base station and said user handsets, each said user handset having a time base and means for controlling it power transmission, each handset having a local oscillator, said base station having an order wire channel for transmitting a reference sounding signal, the improvement comprising:

means for measuring the time base error of each handset at said base station and transmitting time base correction information from said base station to each handset, respectively, and correcting said tune base using said tune base correction information,

means for measuring the power of the reference sounding signal and performing instantaneous compensation of the handset transmit power so as to avoid signal interference, and

means at each handset for receiving said reference sounding signal and phase-locking said local oscillator to said reference sounding signal.

4. In a spread spectrum orthogonal code division multiple access (OCDMA) communication system having at least one base station and a plurality of user handsets in which a set of orthogonal Radamacher-Walsh (RW) functions are overlaid with a pseudonoise (PN) sequence forming a coded spreading sequence for an information signal, each orthogonal function of said set carries voice data for a single user in said system, a source of selected carrier signals and means to modulate said information signal on said carrier signal to form a transmit signal with said coded spreading sequence on said transmit signal for radio broadcasting between said at least one base station and said user handsets, each said user handset having a time base and means for controlling its power transmission, and wherein the base station transmits a sounding signal, each said handset having a local oscillator, the method of controlling operation of said handsets comprising:

measuring the time base error of each handset at said base station and transmitting time base correction information from said base station to each handset, respectively,

using instantaneous power control of handset to base station link, including measuring the power of the reference sounding signal and performing the compensation of the handset transmit power so as to avoid signal interference,

transmitting a reference sounding signal from said base station,

receiving said reference sounding signal, and

phase-locking said handset local oscillator to said reference sounding signal.