MXPA01000954A - Method and system for providing personal base station communications - Google Patents

Abstract

A portable phone (236) may operate inexpensively as a cordless phone when in a micro-cell generated by a micro-base station (202),or flexibly as a cellular phone when it leaves the micro-cell and is served in a macro-cell generated by macro-base station (204) operating on the same frequency. When a mobile phone (222), served by the macro-base station (2042), drives by, the signals from the micro-base station (202) (intended for the portable phone 236) drown out the signals from the macro-base station (204). This invention solves the problem by having the micro-base station (202) receive, delay, and retransmit (on a 50%duty cycle -- half the time receiving and half retransmitting) all signals transmitted by macro-base station (204), in addition to transmitting its own signal. The delay appears to the mobile station (222) as a resolvable multi-path delay, and it continues to be able to receive the signal intended for it.

Description

METHOD AND SYSTEM FOR PROVIDING COMMUNICATIONS TO A PERSONAL BASE STATION Field of the Invention The present invention relates to wireless communication systems. More particularly, the present invention relates to a new and improved method and system for providing communications to a personal base station within the coverage area of a cellular base station.

Antecedents of the Invention Since wireless communication systems have become more relevant in society, the demands of a larger and more sophisticated service have grown. To meet the capacity requirements of wireless communication systems, multiple access techniques have been developed for a limited communication source. One of several techniques for facilitating communications, in which a large number of users of the system are present, is the use of code division multiple access modulation (CDMA) techniques. Other multiple access techniques are known in the art, such as time division multiple access (TDMA), and frequency division multiple access (FDMA). However, the CDMA spectrum diffusion modulation techniques have significant advantages over these other modulation techniques for multiple access communication systems. In the North American Patent No. 4,901, 307, filed on February 13, 1990, entitled "MULTIPLE DISTRIBUTION ACCESS COMMUNICATION SYSTEM USING REPETI DORAS DE SATÉLITE OR TERRESTRES", granted to the assignee of the present invention and incorporated into the same as a reference, the use of CDMA techniques in a multiple access system is described. In US Patent No. 5, 103,459, filed on April 7, 1992, entitled "SYSTEM AND METHOD FOR GENERATING FORMS OF SIGNAL ON IN A CELLULAR TELEPHONE SYSTEM CDMA", granted to the assignee of the present invention and incorporated into the same as a reference, the use of CDMA techniques in a multiple access communication system is further described. In the North American Patent No. 5, 101, 501, filed on March 31, 1992, entitled "METHOD AND SYSTEM FOR PROVIDING A SOFT COMMAND IN COMMUNICATIONS IN A CDMA CELLULAR SYSTEM", granted to the assignee of the present invention and incorporated into the same as a reference, the use of CDMA techniques in a multiple access communication system is also described. The teachings of the aforementioned patents have been applied to relatively large wireless communication systems, such as cellular telephone systems, which, in turn, interface with a public switched telephone network (PSTN). In this way, the user of a subscriber station, such as a cell phone, can generally originate or receive calls from any other communication device connected to the PSTN, as long as the subscriber station is located within the geographic coverage area of any wireless base station belonging to the cellular system. The coverage area for these base stations generally extends several miles. The base stations of these cellular systems are generally referred to as "macro" base stations, and their respective cell sites are referred to as "macro" cell sites. Due to the relatively high cost of cell phone service through these base stations, compared to the traditional landline telephony service, currently it does not represent an effective cost to use a cell phone for all telephone communications that a person wishes to make. Therefore, cell phone users generally use the cell phone only when a conventional landline connection is not available, such as when such people are away from their home or office. This is inconvenient, since the user must change phones, when entering or leaving his home and office. Some cordless telephones of the prior art, have suggested an operation in a cellular / wireless way in a double way, in a common device. These cordless phones of the prior art provide cellular service to the PSTN, through macro cells of a cellular communication system, and wireless service to the PSTN, through a "micro" base station, such as a cellular / wireless unit in double mode. The dual-mode wireless / cellular headset automatically switches between the cellular operation mode and the standard wireless operation mode, as the user moves within the coverage area of the micro base station. Therefore, when the user is away from home, he uses the phone twice in cellular mode, and incurs cellular service charges. However, when the user is within the coverage area of the base unit of the cordless telephone, normally within the home or office, he uses the telephone in a dual mode in wireless mode, avoiding charges for cellular service. One problem with the prior art solution is that since normally dual-mode telephones must operate in two different frequency bands and use two different communication protocols and modulation schemes, said dual mode phones must include expensive additional components. For example, they typically include separate transmission and reception for cellular and wireless signals, complex switches, and special control circuits. These additional components add cost, size and weight to dual mode phones of prior art. What is needed is a communication system that simultaneously provides cellular service and local wireless service, without increasing the peak cost or complexity of the subscriber station.

Summary of the Invention The present invention is a new and improved method and system for providing communications to the personal base station within the "cell" of a cellular base station. As defined and used in the present invention, the term "cell" will refer to a geographical coverage area, while the term "cell-site" will be used to refer to the physical equipment used to perform the communications, for example , one or more base stations. The present invention provides a method and operating system of a base station, wherein the transmission link (base station to the subscriber station) of a macro base station, belongs to a cellular communication system. Operating the personal base station in the same frequency assignment of the macro base station, an operator is not required to use an additional spectrum, in order to provide support to the micro base station. Since an operator has a fixed amount of spectrum assigned to it, and if the operator is using all of its existing spectra, the operator may have to spend a great deal of money to add more cells to release a frequency. Generally, other alternatives, such as obtaining more spectra, are not available to an operator. Although the present invention is described herein with reference to the CDMA system, it is understood that the teachings are equally applicable for other wireless communication schemes, either digital or analogue, regardless of the modulation scheme employed. In the present invention, a first wireless base station is operated in the same frequency band as a second wireless base station. The first wireless base station, a "macro" base station, generates and transmits a first transmission link data signal, a "micro" base station, generates a second transmission link data signal and communicates with a second station. Subscriber The second wireless base station receives the first transmission link data signal and combines it with its own second transmission link data signal to form a combined transmission link data signal, subsequently the second wireless base station transmits the combined transmission link data signal. Therefore, the first subscriber station, which is in communication with the macro base station, has the ability to receive and combine in a diverse manner the transmission link data of the macro base station from the link data signal of the base station. combined transmission transmitted by the micro base station, improving the signal-to-noise ratio that could otherwise occur, in the areas surrounding the micro base station. In a first embodiment of the present invention, the micro base station combines the first transmission link signal with its own second outgoing transmission link signal at the radio frequency (RF). In a second embodiment of the present invention, the micro base station combines the first transmission link signal with its own second outgoing transmission link signal at an intermediate frequency (IF). The present invention also delays the first transmission link data signal received during a predetermined delay period, before combining it with the second transmission link data signal, so that it appears for the first subscriber station, as a Multipath signal that can be decomposed. In order to avoid self-interference, the second wireless base station switches between receiving the first transmission link data signal and transmitting the combined transmission link data signal, in a predetermined change period. In the preferred embodiment, the predetermined change period results in a transmission performance cycle of approximately 50%. Thus, the micro base station does not transmit in substantially continuous form, but rather changes roughly in the "half-interval" of a predetermined time interval, between the transmission of a combined signal and the reception of the first link signal of transmission from the macro base station. In another aspect of the present invention, a power meter in the micro base station measures a power level of the first received delayed transmission link data signal, and, a gain adjuster, adjusts the power level measurement , in order to increase the first transmission link data signal with respect to the second transmission link signal. In the preferred embodiment, the magnification factor is determined according to the received power of the first transmission link signal, as measured by the power meter. This increase is carried out in order to ensure sufficient power of the transmission link data transmitted in the first subscriber station from the macro base station, without unduly degrading the signal-to-noise ratio of the link data. transmission characteristics of the micro base station in the second subscriber station. According to another aspect of the present invention, unacceptable interference from the second subscriber station, which is in communication with the micro base station, through the micro base station, is avoided, either by terminating the communication with the second station. subscriber or executing a connection of the second subscriber station to the macro base station, when the transmit power of the second subscriber station exceeds a predetermined threshold value. In this regard, a frequency control command generator located in the micro base station generates power control commands, wherein each of the control commands indicates an increase or decrease in the transmission power. A transmitter in the pico base micro station transmits these power control commands to the second subscriber station. To avoid excessive interference, the micro base station terminates communication with the second subscriber station, if the micro base station transmits a predetermined number of consecutive power control commands indicating an increase or decrease in transmit power. In an alternative embodiment, the base station informs the second subscriber station of the maximum power that the second peak subscriber station is allowed to transmit, using the micro base station. The second subscriber station is not allowed to exceed this power while in communication with the micro base station. When the second subscriber station using the micro base station reaches this limit, the micro base station will send control commands continuously, so that the second subscriber station has an increase in its output power.; however, the second subscriber station does not increase its transmission power. Subsequently, the micro base station may perceive that the second subscriber station is at the edge of the coverage and releases the call. The micro base station can adjust the maximum amount of power that the second subscriber station is allowed to transmit, monitoring the amount of power that is received from the macro base station. In accordance with another peak aspect of the present invention, the macro base station typically includes means for maintaining extremely accurate time and frequency reference. This is usually achieved by means of a satellite receiver of the Global Positioning System (GPS) or other expensive equipment. However, it can be prohibitively expensive to provide such precision equipment in the micro base station. Therefore, in the present invention, the micro base station obtains the exact time and frequency reference of the macro base station. In this regard, the micro base station includes a demodulator which demodulates the first received transmission link data signal, and means for determining the time reference, to determine a time reference from the first link data signal transmission received demodulated. In addition, the micro base station includes means for determining the frequency reference, to determine a frequency reference from the first demodulated received transmission link data signal.

BRIEF DESCRIPTION OF THE DRAWINGS The features, objects and advantages of the present invention will be better appreciated from the detailed description that will be presented below, provided that it is taken in conjunction with the drawings, in which, the similar reference characters they are identified correspondingly through it, and where: Figure 1 is a graph of the power received as a function of the distance from a macro base station and a micro base station of the present invention; Figure 2 is a general block diagram of the system of the present invention; Figure 3 is a block diagram of a first embodiment of the micro base station of the present invention; Figure 4 is a block diagram of a second embodiment of the micro base station of the present invention; Figure 5A is a graph of an example part of the transmission link of the macro base station, as it is transmitted in an arbitrary time interval; Figure 5B is a graph of an example part of the combined transmission link of the micro base station as it is transmitted in the same arbitrary time interval of Figure 5A; and Figure 6 is a block diagram of an exemplary coding and modulation apparatus of the macro base station.

Detailed Description of the Invention In a CDMA cellular system, as described by the Standard Interim IS-95 Association of the Industry of Telecommunications (TIA) / Electronic Industries Association (EIA), entitled "Mobile Station Compatibility Standard-Base Station for a Dual-Mode Broadband Spectrum Cell Broadcasting System", the transmission link (base station to mobile station) operates on a frequency channel of 1.25 MHz, for example, in accordance with the IS-95 standard, the transmission link of a base station can operate on a particular 1.25 MHz CDMA channel, allocated among a plurality of CDMA channels of 1.25MHz -wide, located within the range of from 869.70 MHz to 893.31 MHz. A single CDMA base station can transmit different information signals for each of its multiple subscriber stations through the same frequency channel 1.25 MHz. The base station CDMA can modulate each respective information signal with a different pseudo-noise (PN) code, which broadcasts the information signal in frequency. Subsequently, a particular subscriber station has the ability to differentiate the information signal of interest to it, by correlating the received signal with the same PN code that was used by the base station, to modulate said signal, thus ceasing to broadcast. only the desired information signal. The remaining part of the information signals, whose codes do not match, do not stop spreading in the bandwidth. As a result, these other information signals contribute to generating noise in the receiver of the subscriber station and represent a self-interference generated by the CDMA system. For similar reasons, the signals from the neighboring base stations also contribute to the generation of noise in the receiver of the base station.

Provided that the ratio of the energy per bit (E) of the signal of the desired information to the noise power spectral density (No) of the operating environment is large enough, the signal of the desired information can be demodulated in successful way. However, when the Eb / N0 of the signal of the desired information is low, such as in the presence of significant interference from other base stations, the error ranges become unacceptably high. For these reasons, as a subscriber station moves from the coverage area of a first base station within the peak coverage area of a second base station, said subscriber station will generally execute a "connection" from the first base station to the second base station, when the signals from the second base station exceed a predetermined threshold value. These general principles are described in greater detail in the aforementioned patents. The same general principles of the acceptable signal to noise ratio also apply to other wireless communication systems. This presents a significant problem, if a personal base station is operated on the same assigned 1.25 MHz frequency channel, than that of the neighboring macro base station. The problem is illustrated in Figure 1. Line 102 represents the time power received in a subscriber station from a macro base station in the form of a function of the distance from the macro base station. Therefore, since a subscriber station which is in communication within the macro base station, moves away from the macro base station, and towards the micro base station, the relative power received from the micro base station is increased. In order to be inexpensive, a personal base station is relatively small and does not have the resources to accept a connection from a neighboring macro base station, even when it is desired to accept it. In addition, if the micro base station had the resources to accept the connections, it might not be desirable to operate the micro base station in a way, in which it accepts all connections or calls from the base station. Therefore, at some distance, designated "D", the power received from the micro base station, which represents interference for the communication of the subscriber station with the macro base station, becomes large enough to cause error ranges of unacceptably high demodulation. An example of the dilemma illustrated in Figure 1 is when a user of a mobile phone, who is communicating with a macro base station through a mobile phone in his car, is moving through a house that has a personal base station which operates its transmission link in the same frequency assignment as the transmission link of the macro base station. Since the personal base station belongs to the owner of the house, generally said base station is programmed to accept only origins of calls or connections from "local" subscriber base stations (for example, those associated with the micro base station), and not from "external" base stations (for example, those not associated with the micro base station). This can be achieved, for example, by recognizing the micro base station identification of the mobile station, such as the IMSI or ESN, which is allowed to make an origin or make a connection. This can be verified, in order to avoid fraud by the use of an authentication key or a Personal Identification Number (NI P), shared by the "local" subscriber base station and the micro base station. The micro base station can also be informed through the network of authod mobile stations and the micro base station can recognize these mobile phones through its IMSI or ESN. Therefore, as the telephone user approaches the house, the interference from the personal base station could, without the use of the present invention, become unacceptably.

I. Micro base station repeater The present invention provides a method and apparatus for the operation of a personal base station, wherein the transmission link of the personal base station is on the same frequency channel as the transmission link of the base station. a macro base station that belongs to a neighboring wireless communication system. The solution is for the personal base station to "listen" to the subscriber station during a part of the time when the macro base station is transmitting on its transmission link.

Subsequently, the base station combines the transmission link data of the macro base station with its own output transmission link data. The two signals can be increased relative to one another, and combined so that a passing subscriber station could demodulate its desired information signal, which originated in the macro base station, from the combined signal transmitted through of the micro base station. In Figure 2, a general review of the system 200 of the present invention is illustrated. In Figure 2, a mobile station 222 is shown in communication with the macro base station 204. Therefore, the desired information signal for the mobile station 222, as part of the transmission link data of the macro base station, is transmitted by the transceiver (XCVR) 218 by means of the antenna of the macro base station 216 and the path of the transmission link 226. The base station 222 receives the data of the transmission link of the macro base station, by means of the antenna 220. The mobile station 222 also transmits a reverse link signal through the antenna 220 and the reverse link path 228, which is captured by the antenna of the base station macro 216 and is received by XCVR 218 Therefore, the mobile station 222 could generally correspond to the "external" subscriber station, which is not associated with the micro base station 202. In Figure 2, a portable station 2 is also shown. 36, in communication with the base station 202. As shown in Figure 2, a portable station 236 is in communication with the base station 202. The transmission link signal transmitted by the base station 202 is received. by the portable station 236 in the transmission link path 232. The portable station 236 also transmits a reverse link signal in the reverse link path 234, which is received by the base micro station 202. Therefore, the portable station 236 could generally correspond to the "local" subscriber station which is associated with the micro base station. The portable station 236 may also have the ability to receive some signal from the macro base station 204 in the transmission link. However, the present invention assumes that the mobile station is not in soft control with the macro base station. Therefore, the macro base station 204 may provide some interference to the portable station 236, and the portable station 236 may not obtain signals with the desired user information from the macro base station 204. Similarly, the macro base station 204 may be receiving some signal from portable station 236; however, it is not processing the reverse link from the portable station 236, and, therefore, the receiving signal is interference. It should be noted that both the mobile station 222 and the portable station 236 could be any type of wireless subscriber station, whether mobile, portable or any other. However, for purposes of clarity and simplicity of illustration, in the present invention they will be referred to as a mobile station 222 and a portable station 236. The micro base station 202 also receives the transmission link data signal transmitted by the macro station base 204 through the transmission link path 224. The signal is captured by the antenna of the base station 206 and routed by the duplexer 208 to the combiner 214. The combiner 214, combines the transmission link data signal transmitted by the base station macro 204, with the transmission link data of the micro base station. The resulting combined transmission link data signal is subsequently transmitted through the duplexer 208 and the antenna 206. The mobile station 222 receives the combined transmission link data signal through the transmission link path 230. Therefore, the mobile station 222 has the ability to receive and combine the transmission link data of the macro base station in a diverse manner through both the transmission link path 226 and the transmission link path 230, improving the signal for the noise ratio, which could otherwise occur in the vicinity of the base micro station 202. The same combined transmission link data signal is also received by the portable station 236 through the path of transmission link 232. Likewise, the duplexer 208 can serve another function to separate the transmission frequency of the portable station 236 of the transmission frequency of the base station 202. The signal that has been received from the portable station 236 is subsequently fed to a receiver and a demodulator, which are not shown in Figure 2. The receiver and demodulator, they are similar in shape to those used in the macro base station 204. However, the micro base station 202 is usually designed to handle only a single call or few calls, therefore, the receiver and demodulator of the micro base station 202, they can be much simpler in design than the receiver and demodulator in the macro base station 204. In a first embodiment of the present invention, the micro base station 202 combines the transmission link signal of the macro base station with its own signal from the base station. Output transmission link in the radio frequency (RF). Figure 3 illustrates this first embodiment of the present invention. The transmission link signal of the macro base station is received by the base micro station 202 through the transmission link path 224. The antenna 206 passes this transmission link signal received through the duplexer 208 to the transmit element. delay 304. The delay element 304 introduces a predetermined time delay, which will be described in more detail below, into the received transmission link signal. The delayed transmission link signal is passed to the increment element 320, which increments the delayed transmission link signal according to the increment factor, g, generated by the gain adjustment element 312. The increment element 320 may contain attenuators, amplifiers, or both, in order to adjust the level of the signal from the macro base station 204 to the correct level. The construction of these elements is well known in art. In the preferred embodiment, duplexer 208 is a switch as shown in Figures 3 and 4. As indicated above, this can be combined with a more conventional duplexer, to allow antenna 206 to be used to receive transmissions of portable station 236. During use, duplexer 208 separates received transmissions from portable station 236 and feeds them to receiver 324. This is not shown in the Figures, as it is well known in the art. In the preferred embodiment, the increase factor, g, is determined according to the received power of the transmission link signal, as measured by the power meter 310, as well as the gain of the transmission link signal of the micro base station, as transmitted by the transmitter (XMTR) 304. The increment factor, g, provides a means for increasing the transmission link signal of the received macro base station, with respect to the transmission link data signal of the micro base station, which has been converted and amplified by XMTR 314. This increase is carried out in order to ensure a sufficient ED / N0 of the data of transmission link of the base station macro relayed in the base station 222, without unduly degrading the ED / No of the transmission link data proper to the micro base station in the portable station 236 of the user of the micro base station. The transmission link signal of the increased macro base station is combined in the combiner 322 with the transmission link signal of the micro base station generated by XMTR 314. The resulting combined transmission link signal is provided through the duplexer 208 to the antenna 206 which is radiated through the transmission link paths 230 and 232. In a second embodiment of the present invention, the micro base station 202 combines the transmission link signal of the macro base station with its own output transmission link signal at an intermediate frequency (IF). Figure 4 illustrates this second embodiment of the present invention. In this second embodiment, the transmission link signal of the macro base station is received by the base micro station 202 through the transmission link path 224. The antenna 206 passes this received transmission link signal through the duplexer 208, to receiver 403 where the signal is converted downward to IF. The transmission link signal of the macro base station IF is subsequently passed to the delay element 304 which introduces a predetermined time delay in the transmission link signal of the macro base station I F. The transmission link signal of the macro IF delayed base station is passed to the increment element 320 which increases the delayed transmission link signal according to the increment factor, g, generated by the gain adjustment element 312. In the preferred embodiment, the increase factor, g, is determined according to the received power of the transmission link signal as measured by the power meter 310, as well as the gain of the transmission link signal of the micro base station IF as amplified by the preamplifier 415. The increment factor, g, provides a means for increasing the transmission link signal of the macro base station IF, co n with respect to the transmission link data signal of the micro base station IF, which has been amplified by the preamplifier 415. The transmission link signal of the increased macro base station IF, is combined in the combiner 322 with the transmission link signal of the micro base station IF. The resulting combined transmission link signal is provided to the transmitter 414 where it is up-converted, amplified and transmitted through the duplexer 208 through the antenna 206, where it is radiated through the transmission link paths 230 and 232. As a result, the transmission power of the transmission link of the macro base station 204 follows the curve 106 in Figure 1. Specifically, the effective power density (or power received by the mobile station 222) of the transmission link of the macro base station 204 follows the curve 106 which is very close to that radiated by the macro base station 204, only (curve 102) until the mobile station 222 approaches the macro base station 202. Up to this point, the mobile station 222 has the ability to receive both the micro base station 202 and the macro base station 204, and this result is a little above curve 102. If the mobile station 222 is very close to the base station 202, then the power is essentially only that of the base station 202 and follows the curve 104. Since the transmission link the macro base station 204 is in the same frequency allocation as the transmission link of the micro base station 202, it is important for the present invention that the micro base station 202 is not "listening" to the macro base station 204 while the micro base station 202 is transmitting on its own. This could cause, in a clear way, an unacceptable self-interference. Therefore, the present invention provides a synchronization scheme which avoids self-interference. Figures 5A and 5B illustrate the synchronization scheme of the present invention. Figure 5A is a graph of the transmission link energy of the macro base station over a period of time. In the example illustration, the transmission link of the macro base station has been illustrated through the time interval T0-T5. The data in the time interval T0-T5) are represented in Figure 5A as from C1 to C3, respectively. As can be seen in Figure 5A, the macro base station can transmit data continuously through the time interval T0-T5, as it could normally be done in a system that complies with the IS-95 standard. Therefore, Figure 5A represents a generic example of the transmission link signal of the macro base station over time, which would be observed in the path of the transmission link 224 of Figures 2, 3 and 4. The Figure 5B is a graph of the transmission link energy of the micro base station through the same time intervals as Figure 5A. The shaded portions of the time slots indicate the times when the micro base station 202 is not transmitting, but rather is "listening" for the transmission link signal of the macro base station, as shown in Figure 5A. The unshaded portions represent the times when the base station 202 is transmitting the combined signal comprising the transmission link data of the base station and the transmission link data of the base station macro. As can be seen in Figure 5B, the micro base station 202 does not transmit substantially continuously through the time interval T0-T5, but rather connects rigorously in the "half interval" of each time interval between the transmission of a combined signal and the reception of the transmission link signal of the macro base station. In the preferred embodiment, a short guard period is also provided, during which the micro base station is neither transmitting a combined signal nor receiving the transmission link signal from the macro base station. This guard period is represented in Figure 5B by the brief blank periods between successive shaded and unshaded blocks. Therefore, Figure 5B represents a generic example of the micro base station combined with the transmission link signal during the time in which it could be observed in the transmission link paths 230 and 232 of Figures 2, 3 and 4. In the preferred mode, the synchronization scheme of the Figure 5B is achieved through the delay element 304, and the duplexer connection means 208. Alternatively, the receiver 324 (Figure 3) or 403 (Figure 4), and the transmitter 314 (Figure 3) or 414 ( Figure 4), respectively, can implement the connection means, alternatively covering the transmission and reception signals. In the preferred embodiment, during the time represented by the shaded periods of Figure 5B, the duplexer 208 routes the transmission link signal of the macro base station that enters the delay element 304 and the receiver 324 (Figure 3) or 403 (Figure 4). Therefore, the micro base station "listens" for the first half of each transmission link data interval C-i-Cs of the macro base station of Figure 5A. As mentioned above, the delay element 304 introduces a predetermined time delay in the transmission link signal received from the macro base station. This predetermined time delay is equal to the switching period, for example one half of the interval. During the time periods represented by the non-shaded portions of Figure 5B, the duplexer 208 routes the combined output link signal to the antenna 206 for radiation through the transmission link paths 230 and 232. thus, the combined signal transmitted by the micro base station, as represented by the non-shaded portions of Figure 5B, includes the transmission link data of the macro base station from the immediately preceding half-interval. Since the base station 202 can not "hear" the transmission link of the base station macro 204, when the base station 202 is transmitting itself to the base station 202, it will "lose" essentially half the data transmitted in the transmission link of the base station macro 204. This means, that it will not have the capability of delaying and retransmitting the second half of each transmission link data interval C1-C5 of the macro base station 204. Therefore, , the period of the connection interval is preferably chosen, such that the "lost" data has a minimal effect on the ability of the mobile station 222 or the portable station 236 to demodulate and decode the combined transmission link signal. The determination of an acceptable switching period depends to a large extent on the design of the transmission link used by the macro base station 204 and the micro base station 202 at their respective forward links. In Figure 6, an exemplary transmission link coding and modulation scheme for a transmission traffic channel of the macro base station 204 or the base micro station 202 is illustrated, and is based on the IS-95 standard. It should be noted that other communication channels, such as pilot and synchronization channels, can be encoded and modulated in a similar manner. However, for purposes of clarity and simplicity, the operation of the traffic channel will be described in the present invention. In Figure 6, the data of the transmission link information that has been multiplexed into structures, is presented to the convolution encoder 602. In the example mode, the convolution code is in the range 1/2, thus generating two code symbols for each data bit entering the encoder 602. Also, in the exemplary embodiment, the encoder 602 has a restricted length of nine. Convolution coding, as is known in the art, comprises the addition of two derivation modules selected from the sequence of delayed time entry data in series form. The length of the delay of the data sequence is equal to K-1, where K is the restricted length. Therefore, the output of the convolutional encoder 602 is twice the range of the input, with each of the resultant convolutionally encoded modulation symbols being dependent on other adjacent modulation symbols according to the constrained length. Clearly, other code ranges and restricted lengths could be used. The output of the convolutional encoder 602 is presented to the symbol repeater 604. In the exemplary embodiment, the symbol repeater 604 repeats each convolutionally encoded modulation symbol according to the range of information data, resulting in a output that has a constant range of modulation symbols. For example, if the range of information data is in a range as high as 9,600 bps, there is no repetition of the symbol. In a range of information data from the middle of the highest range, or 4,800 bps, each code symbol is repeated once (each symbol occurs twice consecutively). In a data range of one quarter of the highest range, or 2,400 bps, each code symbol is repeated three times. And in an information data range of one eighth of the highest range, or 1, 200 bps, each code symbol is repeated seven times. As can be seen, this example would result in a constant range of modulation symbols of 19,200 modulation symbols per second, with the output from the symbol repeater 604. Other groups of ranges can also be used clearly. The output symbols of the symbol repeater 604 are presented to the interstratifier of blocks 606, which in the example mode of a traffic channel, spans 20 ms, which is equivalent to 384 symbols of modulation in the range of symbols Example modulation of 19,200 symbols per second. The interlayer formation is 24 rows by 16 columns. The symbols are written in the formation of the interstratifier of block 606 by columns, and are read in a pattern that largely disperses the symbols of adjacent modulation. In an example case of a transmission traffic channel, the interstratified modulation symbols read from block interleaver 606, are input to the addendum of two modules 608, where they are covered by the long code PN sequence assigned to the mobile station 222. The long code generator 614 generates a PN sequence in a range of 1.2288 Mcps, which is shown in descending order at 19,200 ksps by the decimator 616, to coincide with the range of the modulation symbol. The PN sequence is further shown in descending order by the decimator 618 to cover or randomize the locations of the power control bits that are drilled in the transmission traffic channel by the multiplexer (MUX) 610. Subsequently, the data from Transmission traffic are broadcast orthogonally with respect to the other front channels, by means of a Walsh function of the assigned traffic channel that has a fixed chip range of 1.2288 Mcps in the adder of two 612 modules. Subsequently, the data of Transmission traffic are broadcast in quadrature form by means of the I-channel and the PN diffusion sequences of the Q channel PNi and PNQ, respectively, into channel data of two modules that are filtered in the filters 624 and 626 respectively, and subsequently converted in ascending form to the conveyor frequency, fc, by means of mixers 628 and 630. Subsequently, the RF signals of the I and Q channels are combined Ades in the combiner 632, and produced for an amplification of power and additional radiation through the antenna 216 (see Figure 2). In Figure 6, the exemplary coding and modulation scheme, which is mentioned in the aforementioned US Pat. No. 5,103,459, is described in more detail. The example coding and modulation scheme described above is very robust and error-resistant. As a result, the amount of time to "listen" may be a bit less than a 50% performance cycle without significant data loss. Therefore, the switching period used by the present invention in a communication system employing a powerful error coding scheme, it can be variable in a range greater than that used in a system that has a narrower bandwidth, and that therefore must use less powerful schemes. For example, in the example mode described above, each information bit has been encoded by a 1/2 convolutional encoder 602. Therefore, each bit has at least two modulation symbols, with lower ranges having even more redundancy added by the symbol repeater 604. In addition, the adjacent modulation symbols are scattered in time, largely by the interlayer of block 606. Additionally, the restricted length of the convolutional encoder 602 and the uniqueness of the coding symbols used as a whole are added to the robustness of the coding scheme. As a result, assuming that the energy of the transmitted signal is sufficient, the switching period can be of the order of milliseconds without a significant loss of data. Assuming a structure of 20 ms, the commutation period can approach 10 ms. Alternatively, the commutation period may be shorter in the order of the duration of a single modulation symbol, in which case, each of the other symbols would be lost. In a still preferred embodiment, the switching period may be even shorter, in the order of the duration of a single PN chip. Even in another mode, the switching period can be random. The determination of an acceptable switching period depends largely on the design of the transmission link used by the macro base station 204 and the micro base station 202 in their respective transmission links. In the example of a system according to the IS-95 standard, the period Tj +? - Tj must be long enough so that the delay is greater than a PN broadcast chip (so that the multiple path created by the base station 202, is separated by at least one chip), and so that the transmitted spectrum is that of the original IS-95 signal. However, the period Tj + -Tj should not be so long, so that the mobile station 222 does not have the ability to track the phase and synchronization of the base stations. There is an additional consideration with IS-95 systems with orthogonal transmission links separated by Walsh functions. When the mobile station receives only a part of a Walsh function, then some orthogonality is lost, and the signal required for the noise ratio increases due to the coupling between the transmission link Walsh channels. To maintain orthogonality, the connection could be made to each Walsh or exact multiple function of the time span of a Walsh function. To be even more specific in the context of an IS-95 system, as shown in Figure 6, the locations of the power control bit are randomized and multiplexed in the data stream, as shown in the Figure 6. These power control bits occupy one or two Walsh functions in each 1.25 ms in the transmission link. For the IS-95 system, the connection time could be randomized, so that the mobile station 222 receiving the macro base station 204 receives all the power control bits. The exact duration of the connection and the exact time of the connection that is chosen depends on these and other aspects, such as the complexity of the delay 304. It should be noted that the mobile station 222 (see Figure 2), which is in communication with the base station macro 204, it continues to transmit the reverse link data to the base station macro 204, through the reverse link path 228. Although the mobile station 222 is receiving the combined transmission link signal from the micro station base 202 through the transmission link path of the micro base station 230, the micro base station 202 does not demodulate the signal of the mobile station 222, although the signal from mobile station 222 may be strong enough to be demodulated. In other words, as described in the aforementioned US Patent Number 5, 101, 501, the mobile station 222 does not execute a connection to the base micro station 202 although the strength of the pilot signal of the micro base station 202 may exceed the nominal threshold value for the connection. The combined transmission link signal received from the base station 202 through the transmission link path 230, appears at the mobile station 222 to be very similar to any other multi-path component originating in the macro base station 204, except that the signal will be "cut" in the middle interval. Therefore, the mobile station 222, which in the preferred embodiment has the ability to combine multiple path signals in different ways, will be sufficiently aided by the additional power provided by the transmission link path 230 to avoid error ranges. of unacceptably high demodulation. Furthermore, since the micro base station 202 retransmits any signal it receives in the particular frequency assignment, for example, the transmission link of the complete macro base station, in addition to more "external" mobile units 222, does not increase the load on the base station. the micro base station 202. In many cases, the micro base station 202 will be within the coverage area of a macro base station 204. In this case, it retransmits only the transmission link of a macro base station 204. However, such a as described in U.S. Patent No. 5, 101, 501, filed on March 31, 1992, entitled "METHOD AND SYSTEM FOR PROVIDING A SOFT COMMAND IN COMMUNICATIONS IN A CDMA CELLULAR SYSTEM", all CDMA base stations transmit on the same frequency, and a smooth command can be used by mobile stations. In this case, the micro base station 202 will retransmit the signals of the base stations it is receiving, with a power proportional to the force in which they are being received by the 15 micro base stations 202.

II. Reference of Time and Frequency. According to another aspect of the present invention, the micro base station 202 demodulates at least one logical channel of the transmission link signal of the base station 204, in order to obtain a stable reference of time and frequency. As explained above, the macro base station 204 normally includes means for maintaining an extremely accurate time and frequency reference. Generally, this is achieved by means of a satellite receiver of the Global Positioning System (GPS) (not shown) or other expensive equipment. However, it can be prohibitively expensive to provide such precision equipment in the base station 202. Therefore, in the present invention the base station 202 obtains the exact time and frequency reference from the macro base station 204. Referring to FIG. again to Figure 3, the antenna 206 captures the transmission link signal of the macro base station from the transmission link path 224, and routes it to the receiver (RCVR) 324 through the duplexer 208. The receiver 324 converts in descending form the RF signal, and passes it to the demodulator (DEMOD) 326. The demodulator 326 searches, acquires and demodulates the pilot channel that is transmitted as part of the transmission link signal of the macro base station. In the exemplary CDMA system, this pilot signal can be used to obtain an initial synchronization of the system and to provide a robust time frequency and base tracking of the transmission link signal of the macro base station. Likewise, in the exemplary CDMA system, each base station transmits a synchronization channel which uses the same PN and PN phase as the pilot tube channel and can be demodulated whenever the pilot channel is being tracked. This synchronization channel carries a message containing the identification of the macro base station 204 and the exact compensation of the pilot PN carrier phase of the macro base station 204.

This synchronization information is passed from the demodulator 326 to the time and frequency unit (TFU) 330. Subsequently, the TFU 330 has the ability to determine the exact System Time and obtain a stable frequency reference of the macro base station 204. Subsequently, the TFU 330 provides this synchronization and frequency information to the transmitter 314 and the receiver 324, and provides synchronization information to the duplexer 208, if the duplexer 208 is performing the connection function. In the context of the IS-95 system, the micro base station 202 may not need to demodulate the synchronization channel of the macro base station 204, to obtain the identification of the macro base station and the compensation of the phase of the pilot PN carrier. This is because the micro base station 202 does not move, and this information is static. Therefore, this information can be supplied to the base station 202 through other means, such as the installer of the base station 202. The same techniques are applicable to the embodiment of Figure 4, with respect to the receiver 403. and the transmitter 414. Subsequently, the micro base station 202 can track the pilot channel of the macro base station continuously, or it can "roll free" for a predetermined period of time, and obtain updates of the System Time and reference of often only periodically.

It should be noted that while aspects of the time and frequency thereof have been described in the present invention with reference to an exemplary CDMA system, the teachings of the present invention are equally applicable to other communication systems, either digital or digital. analog, and 25 regardless of the modulation scheme or channeling used. For example, the present invention can also be used in a communication system where the pilot channel of the macro base station carries a System Time preference by itself. Additionally, the pilot channel may not be on the same conveyor frequency or time channel as any other of the transmission link channels. The present invention is not intended to be limited to the specific examples shown therein, and one skilled in the art can apply its teachings to a wide variety of communication systems.

III. Power Control of the Micro Base Station. According to another aspect of the present invention, the micro base station 202 controls the reverse link power level of the portable station 236, to avoid excessive interference with the reverse link signals of other subscriber stations, such as the mobile station. 222, which are received in the base station macro 204. As is known in the art, the wireless communication system 200 can use a combination of closed loop and open circuit power control methods to maximize capacity and avoid interference excessive between subscriber stations. In the open circuit power control methods, the power transmitted by the pilot signal is measured as it is received in the subscriber station. Subsequently, the subscriber station adjusts its transmission power inversely in response; the weaker the received signal, the stronger the transmitter power of the subscriber station. In closed circuit power control methods, the cellular site transmits power adjustment commands to the subscriber station to nominally increase or decrease the transmitter power of the subscriber station by a predetermined amount. In US Patent Number 5,056, 109, filed on October 8, 1991, entitled "METHOD AND APPARATUS FOR CONTROLLING THE TRANSMISSION POWER IN A CDMA CELLULAR MOBILE TELEPHONE SYSTEM", granted to the assignee of the present invention and incorporated therein. as a reference, a power control system and method is described. In the aforementioned patent, the combination of the open and closed circuit power control is used to adjust the transmit power of all mobile stations 222 that are in communication with the macro base station 204, to reach the base station macro 204 at substantially the same predetermined power level. The same power control techniques can be used to control the transmit power of all portable stations 236 that are in communication with the base station 202, so that it reaches the base station 202 substantially at the same predetermined power level. However, since the portable station 236 will not normally be in communication with the macro base station 204, provided that it has satisfactory communications with the base station 202 (to avoid access charges of the cellular system), the macro base station 204 will not have the ability to use closed loop power control commands to instruct portable station 236 to "deviate" its transmitting power. As shown in Figure 2, the power received from the micro base station 202 is weaker than that of the portable station 236 which moves further away from the micro base station 202. As a result of the power control of both the circuit open as closed circuit, the portable station 236 communicating with the microcell 202, will transmit sufficient power to be received by the microcell 202. As a consequence, since the portable station 236 moves further away from the micro base station 202, it could continue to increase its power to a level that could cause unacceptable interference in the reverse link path 228. In the present invention, this unacceptable interference is avoided by the base micro station 202, either by terminating communication with the portable station 236 or executing a connection of the portable station 236 with the macro base station 204, when the power of tra The transmission of the portable station 236 exceeds a predetermined threshold value. In a first embodiment, the micro base station 202 determines by itself when the transmit power of the portable station 236 may be too high. In this first mode, applicable for either Figure 3 or Figure 4, the reverse link signal of portable station 236 is received by antenna 206 and passed to receiver 324 (Figure 3) or receiver 403 (Figure 4). The receiver 324 or 403 downconverts the inclination of the received reverse link signal as described above, and passes it to the demodulator 326. The power control command generator 332, measures the average power of the link signal demodulated inverse of portable station 236, compares said average power to a desired threshold value, and generates either a "forward in" or "forward in downward" command to transmit to portable station 236 through the transmitter 314 (Figure 3) or 414 (Figure 4), in the manner described in the aforementioned US Patent Number 5,056, 109. Intuitively, since portable station 236 travels away from the micro base station, the average power of the reverse link signal is measured by the power control command generator 332 which will tend to decrease due to path loss. In response, the power control command generator 332 will transmit a series of "forward" commands to the portable station 236. In this first mode, the power control command generator 332 keeps track of how much It is often necessary to transmit a "forward" command to the portable station 236. If it transmits more than a predetermined number of commands "forward in ascending order" in a power control command sequence, corresponding to the condition where the portable station 236 is having to be transmitted at a relatively high power level in order to provide a sufficient reverse link signal through the reverse link path 234, the micro base station 202 will terminate the communication with the portable station 236 or will execute a connection of the portable station 236 with the macro base station 204. For example, if the micro is The base station transmitted K power up commands in a group of power control commands N, then the micro base station can determine that the personal station has exceeded the desired range. In a second embodiment, the transmit power of the portable station 236 is limited to a predetermined maximum level when communicating with the micro base station 202. This can be accomplished by rules previously set in the programming of the portable station 236, so that when the portable station is using the micro base station 202, its transmit power is limited to the predetermined maximum level. It should be noted that portable station 236 will not perform such a limitation when in communication with macro base station 204.

This power limitation can easily be achieved by one skilled in the art, for example, by modifying the teachings of the aforementioned US Patent Number 5,056, 109, causing the portable station 236 to ignore the commands "divert in ascending order" once that its transmission power has exceeded the predetermined maximum level while in communication with the base station 202. In the US Patent Number 5,452,473, entitled "CORRECTION AND LIMITATION OF TRANSMISSION POWER, INVERSE LINK IN A RADIOTELEPHONE SYSTEM", filed on September 19, 1995, assigned to the assignee of the present invention and incorporated therein as a reference, a circuit designed to ignore the commands "divert in descending order" is described after the transmit power of the portable station 236 exceeds a predetermined threshold value. In this mode, the micro base station 202 will have the ability to perceive that the portable station 236 is at the edge of the cellular coverage, noting that the portable station 236 has not complied with a series of commands to "divert in ascending order". The micro base station 202 can subsequently release the call. However, a conventional maximum power level could be used by the portable station 236, when in communication with the macro base station 204. The power limitation of the portable station 236 can also be achieved by a command from the micro base station 202 which indicates portable station 236 that limits its transmission power to a maximum level. The micro base station 202 can determine this maximum level by monitoring (with the power meter 310 of Figures 3 and 4), the amount of power received from the macro base station 204. The greater the power received from the macro base station 204. , the maximum allowable transmission power of the portable station 236 may be without causing undue interference to the other mobile stations operating within the macro base station cell 204. Alternatively, the portable station 236 may signal the micro base station 202 with a signaling message indicating that it has reached its power limit or a power threshold value. Along with this signaling message, the portable station 236 can indicate the pilot forces of the surrounding base stations, as is done with the existing IS-95 Pilot Force Measure Message, and as described in more detail in U.S. Patent Number 5, 101, 501 mentioned above. This allows the base station 202 to determine whether it connects the portable station 236 to the macro base station 204. The above description of the preferred embodiments is provided to enable any person skilled in the art to make or use the present invention. The various modifications to these modalities will be readily appreciated by those skilled in the art, and the generic principles defined in the present invention can be applied to other modalities without the use of the inventive faculty. Therefore, the present invention is not intended to be limited to the modalities shown therein, but is intended to be in accordance with the broader scope consistent with the new principles and features described therein. Having described the present invention, the content is claimed in the following:

Claims (32)

1. R E I V I N D I C A I N N E S Having described the present invention, it is considered as a novelty and, therefore, the content of the following CLAIMS is claimed as property. 1 . A method for operating a first wireless base station in the same frequency band as that of a second wireless base station, generating and transmitting said first wireless base station a first transmission link data signal and communicating with a first subscriber station, generating said second wireless base station a second transmission link data signal and communicating with a second subscriber station, wherein the method comprises the steps of: a. receiving, in said second wireless base station, said first transmission link data signal; b. combining, in said second wireless base station, said first transmission link data signal received with said second transmission link data signal to form a combined transmission link data signal; and c. transmitting, from said second wireless base station, said combined transmission link data signal. The method as described in Claim 1, further characterized in that it further comprises the step of delaying for a period of delay said first received transmission link data signal. The method as described in Claim 2, further characterized in that it further comprises the step of switching between said receiving step of said first transmission link data signal and transmitting said combined transmission link data signal in a period of commutation. The method as described in Claim 3, further characterized in that said connection of the switching step is carried out in a 50% yield cycle. The method as described in Claim 3, further characterized in that said delay period is greater in duration than that of a PN diffusion chip. The method as described in Claim 3, further characterized in that said switching step occurs only at the limits of the Walsh function. 7. The method as described in Claim 3, further characterized in that said switching period is of a random duration. The method as described in Claim 3, further characterized by additionally comprising the steps of: a. measuring a power level of said first received or delayed transmission link data signal; and b. adjusting said power level of said first transmitted transmission link data signal delayed in response to said measurement step. 9. The method as described in Claim 3, further characterized by additionally comprising the steps of: a. transmitting power control commands to said second subscriber station, each of said power control commands indicating an increase or decrease in transmit power; and b. terminating communication with said second subscriber station if said second base station transmits a predetermined number of consecutive power control commands indicating an increase in transmit power. 10. The method as described in Claim 3, further characterized by additionally comprising the steps of: a. transmitting power control commands to said second subscriber station, each of said power control commands indicating an increase or decrease in transmit power; and b. executing a connection of said second subscriber station to said first base station, if said second base station transmits a predetermined number of consecutive power control commands indicating an increase in transmit power. eleven . The method as described in Claim 3, further characterized in that it further comprises the step that said second subscriber station limits the transmit power to a predetermined maximum level, when in communication with said second base station, said minimum level being lower predetermined to a conventional maximum level used when in communication with said first base station. 12. The method as described in Claim 1 1, further characterized in that it further comprises the step of said second base station transmitting commands to said second subscriber station to limit the transmit power to said predetermined maximum level. 13. The method as described in Claim 1 1, further characterized in that it further comprises the step of said second subscriber station transmitting a signaling message, indicating that said second subscriber station is transmitting at said predetermined maximum level, said second base station. . 14. The method as described in Claim 3, further characterized by additionally comprising the steps of: a. demodulating, in said second base station, said first received transmission link data signal; and b. determining a time reference from said first demodulated received transmission link data signal. 15. The method as described in Claim 3, further characterized by additionally comprising the steps of: a. demodulating, in said second base station, said first received transmission link data signal; and b. determining a frequency reference from said first demodulated received transmission link data signal. 16. A system for providing operations of the personal base station within the coverage network of a wireless communication system, wherein the system comprises: a. a first wireless base station for generating and transmitting a first transmission link data signal in a predetermined frequency band; and b. a second wireless base station for generating a second transmission link data signal, said second wireless base station comprising: 1) a receiver for receiving said first transmission link data signal; 2) a combiner for combining said first transmission link data signal received with said second transmission link data signal, to form a combined transmission link data signal; and 3) a transmitter for transmitting said combined transmission link data signal in said predetermined frequency band. 17. The system as described in claim 16, further characterized in that it further comprises a delay element for delaying for a period of delay said first received transmission link data signal. 18. The system as described in Claim 17, further characterized in that it further comprises switching means for connecting between said receiver and said transmitter in a switching period. 19. The system as described in Claim 18, further characterized in that said switching means connects between said receiver and said transmitter in a 50% performance cycle. 20. The system as described in Claim 18, further characterized in that said delay period is greater in duration to a PN diffusion chip. twenty-one . The system as described in Claim 18, further characterized in that said switching means connects between said receiver and said transmitter only within the limits of the Walsh function. 22. The system as described in Claim 18, further characterized in that said switching period is of random duration. 23. The system as described in Claim 18, further characterized by additionally comprising: a. a power meter for measuring a power level of said first received transmission link signal; and b. a gain adjuster for adjusting said power level of said first measurement of the received transmission link level. 24. The system as described in Claim 18, further characterized in that it additionally comprises a power control command generator for generating power control commands, indicating each of said power control commands, an increase or decrease in the transmission power, and wherein said second base station terminates communication with said second subscriber station, if said second base station transmits power control commands K which indicate an increase in transmission power within a group of power control commands N, where K is a predetermined number less than N. 25. The system as described in Claim 18, further characterized by additionally comprising a power control command generator for generating power control commands, each of said power control commands indicating an increase or decrease in the power of the power control. transmission and wherein said second base station executes a connection of said second subscriber station to said first base station, if said second base station transmits a predetermined number of consecutive power control commands, indicating an increase in transmit power. 26. The system as described in Claim 18, further characterized in that said second subscriber station limits the transmit power to a predetermined maximum level, when in communication with said second base station, said predetermined maximum level being less than a conventional maximum level. used when in communication with said first base station. 27. The system as described in Claim 26, further characterized in that said second base station transmits commands to said second subscriber station to limit the transmit power to said predetermined maximum level. 28. The system as described in Claim 26, further characterized in that said second subscriber station transmits a signaling message, indicating that said second subscriber station is transmitting at said predetermined maximum level, said second base station. 29. The system as described in Claim 18, further characterized by additionally comprising: a. a demodulator for demodulating said first received transmission link data signal; and b. means for determining the time reference for determining a time reference from said first demodulated received transmission link data signal. 30. The system as described in Claim 18, further characterized by additionally comprising: a. a demodulator for demodulating said received data signal; and b. means for determining the frequency reference for the frequency reference from said demodulated received link data signal. 31 The system as described in Claim 18, further characterized in that said second base station transmits commands to said second subscriber station to have a threshold value, which is used to detect when the output power of the subscriber station exceeds this threshold. threshold value. 32. The system as described in Claim 31, further characterized in that said second subscriber station transmits a signaling message, which indicates that said second subscriber station is transmitting at said predetermined level, said second base station.