Mobile communication system using position location information

The present invention relates generally to wireless communication, and in particular to processing signals based on the location of a remote terminal with respect to a base station.

The wireless communication system includes a plurality of remote terminals and a plurality of base stations. Communication between the remote terminal and the base station can be achieved using one of a variety of multiple access technologies that flow through wireless channels and facilitate a large number of users in a limited frequency spectrum. Examples of multiple access techniques include time division multiple access (TDMA), frequency division multiple access (FDMA), and code division multiple access (CDMA).

CDMA-based systems offer certain advantages over other types of multiple access systems. For example, CDMA allows the frequency spectrum to be reused multiple times, which allows for increased system user capacity. In addition, the use of CDMA technology allows us to overcome the special challenges of wireless channels by mitigating the negative effects of multipathing, such as fading, while also taking advantage of it. CDMA systems are generally designed to implement one or more standards, such as IS-95, CDMA2000, and WCDMA standards, all of which are known in the art and are hereby known. The whole is incorporated.

In CDMA based systems, communication signals are "spread" using pseudo-random (PN) codes. Since the signals share a common frequency spectrum, the individual signals are distinguished by a unique PN code. In a CDMA system, the communication signals are also synchronized with each other.

In a typical CDMA system, the signal transmitted from the base station to the remote terminal is usually referred to as a forward link and includes a pilot signal having a common PN sequence. Since each base station transmits a pilot signal with a time offset from the pilot signal of the adjacent base station, the pilot signals can be distinguished from each other by a remote terminal. At any given time, the remote terminal receives various pilot signals from a plurality of base stations. Using a copy of the PN sequence generated by the local PN generator, the terminal determines the relative phase of the received pilot signal, the PN offset, thereby identifying the corresponding base station that transmitted the pilot signal. The relative phase of the pilot signal is measured by matching or correlating the local PN sequence with the received signal. Correlation to the pilot channel provides a coherent phase reference for demodulating other communication signals transmitted over the forward link. There is no pilot signal transmitted by the remote terminal to the base station, but in what is commonly referred to as a reverse link, the remote terminal is assigned to a unique PN sequence used to transmit the signal to the base station. The base station correlates with the PN sequence assigned to the remote unit in the reverse link signal, which identifies the remote terminal transmitting the signal.

Generally, the search engine used in the correlation process goes through a set of PN offsets, commonly referred to as the search window. The search window often contains the PN offset of the communication signal. For example, the nominal PN offset received at the remote terminal is not only the result of the offset introduced into the pilot signal by the individual base stations, but also due to the relative location of the remote terminal and the various base stations. Because the pilot signals travel different distances from different base stations to the remote terminals, the pilot signals received by the remote terminals are delayed, and therefore only different amounts of time due to the different distances that each of the individual pilot signals travels. Offset. Uncertainty in the PN offset of the received pilot signal causes the remote terminal to search a large search window, consuming scarce resources within the terminal that can be used for other functions.

Determining the nominal PN offset can even be more complicated if the remote terminal is portable and is moving relative to the base station. In a typical mobile terminal, the terminal may go into "sleep mode" to save power and extend battery life. Here, most communication functions, including search engines, are depowered. If the mobile terminal moves relative to the base station before the power is applied again, the nominal PN offset of the pilot signal received from the base station changes. Therefore, even if the nominal PN offset of the pilot signal is known, the nominal PN offset may be different when the remote unit goes to "sleep" or when the mobile terminal wakes up, and a new search needs to be done. This consumes additional remote terminal resources.

A further challenge posed by the movement of mobile terminals is the apparent change in frequency of signals received by both the terminal and the base station while the terminal is moving relative to the base station. is there. This apparent change in frequency is due to a well-known phenomenon called Doppler shift. Frequency changes due to Doppler shift require both mobile terminals and base stations to search using different frequency assumptions and then determine which assumption gives the best results. To reiterate, searching with various assumptions consumes resources.

Therefore, there is a technical need for techniques to provide improved estimation of the nominal PN offset of the pilot signal. In addition, there is a technical need for techniques to improve the choice of frequency assumptions.

<p> Location information about mobile terminals relative to base stations is used to describe methods and devices for improving the performance of communication systems. In addition, information about the speed of the mobile terminal relative to the base station may be used to improve the performance of the communication system. The location information may be used to estimate the nominal PN offset and the set of PN offsets to use in order to process the communication signal. Velocity information may be used to estimate the nominal frequency of the communication signal.</p><p> On one side, the search window for processing the signal in the wireless communication system is determined based on the location of the mobile terminal. The system can determine the location of at least one mobile terminal for a base station with a known location. The distance between the mobile terminal and the base station is calculated based on each of these locations. The nominal PN offset of the signal transmitted between the base station and the mobile station is estimated based on the distance between the mobile terminal and the base station. Using the estimated PN offset, the system determines the search window used to process the received signal.</p><p> According to another aspect, the mobile terminal estimates the nominal PN offset that the signal from the base station would have in response to the reception by the mobile terminal, based on the distance between the mobile terminal and the base station. Using the nominal PN offset, the mobile terminal determines a set of PN offsets to search for signals transmitted by the base station. In addition, the base station estimates the nominal PN offset that the signal from the mobile terminal would have upon receiving reception from the base station , based on the distance between the mobile terminal and the base station . Using the nominal PN offset, the base station determines a set of PN offsets and searches for signals transmitted by the mobile terminal.</p><p> In another aspect, the mobile terminal, the base station, or both, can estimate the nominal frequency of the received signal based on the speed of the mobile terminal relative to the base station. The frequency of the received signal changes due to the Doppler effect caused by the relative movement between the mobile terminal and the base station.</p><p> In yet another aspect, the location of the mobile terminal is determined within the mobile terminal. For example, mobile terminals can receive navigation signals from navigation systems such as GPS, LORAN-C, or other standard navigation systems. Mobile terminals use navigation signals to determine their location with respect to the base station. The mobile terminal may transmit the location to the base station for use by the base station.</p><p> On the other side, the mobile terminal measures the received navigation signal and sends the measurement to the base station. The base station uses the measurements transmitted by the mobile terminal to determine the location of the mobile terminal. The base station may transmit the location to the mobile terminal for use by the mobile terminal. Other features and advantages of the invention will become apparent from the following description of preferred embodiments that illustrate the principles of the invention by way of example.</p>

This application claims the priority of US Patent Provisional Application No. 60 / 407,410. Information about the location and speed of remote terminals in wireless communication systems is used to improve signal acquisition and tracking performance. For example, in CDMA-based communication systems such as TIA IS-95, WCDMA, or CDMA2000, information about the location of mobile terminals with respect to adjacent base stations better provides the nominal PN offset of signals received at mobile terminals and base stations. Can be used to estimate. The PN offset is typically measured on a chip that represents one bit of the signal's PN code. Information about the speed of the mobile terminal relative to the base station can be used to better estimate the nominal frequency of the communication signal due to the Doppler shift. FIG. 1 is a block diagram illustrating a PN offset of a pilot signal transmitted by a CDMA-based wireless communication system. As shown in FIG. 1, base station 102 is communicating with mobile terminal 104, which mobile terminal 104 is shown at two different locations. When the mobile unit 104 is in the first location 110, the communication signal 112 between the base station 102 and the mobile terminal 104 flows through the first distance, represented as D1. When the mobile terminal moves to the second location 120, the communication signal 112 between the mobile terminal 104 and the base station 102 flows a second distance, represented as D2. The second distance D2 is greater than the first distance D1, but it does not have to be this way. In FIG. 1, when the communication signal 112 flows between the mobile terminal 104 and the base station 102 and the mobile unit is in the second location 120, the communication signal 112 is in the mobile terminal in the first location 110. It may flow longer distances and correspondingly longer times.

The difference in signal flow time between the mobile terminal and the base station results in a different PN offset of the received signal compared to the locally generated PN sequence at the mobile terminal. In FIG. 1, the vertical axis 132 represents the strength of the received signal and the horizontal axis 134 represents the PN offset between the locally generated PN sequence of the mobile terminal and the PN sequence of the received signal 112 on a chip. In the CDMA communication system, when the communication signal 112 is received by the mobile terminal 104, a process generally called "correlation" is performed to support the demodulation of the received signal 112. In correlation, locally generated PN sequences, or codes, are shifted in phase or time until the PN sequences, or codes, of the received signal 112 match.

When the locally generated PN code correlates with the PN code of the received signal 112, there is a peak power, or maximum power, detected by the received signal strength. For example, when the mobile terminal is in the first location 110, the phase of the locally generated PN code is the quantity PN-offset represented by 136._D1It is offset to and becomes the power peak of the received signal strength represented by 138. When the mobile terminal 104 moves to the second location 120, the PN offset of the communication signal 112 received by the mobile terminal is different. In FIG. 1, graph 140 illustrates the PN offset of the pilot signal transmitted from the base station 102 to the mobile terminal 104 located at the second location 120. As illustrated in Graph 130, the correlation between the locally generated PN code and the PN code of the received signal 112 is represented by 142 PN-offset._D2It occurs at the peak of the power of the received signal strength represented by 144.

The signal 112 travels a longer distance when the mobile terminal is at the second location 120 than when it is at the first location 110, so the PN-offset_D2Is PN-offset_D1Will be larger than. The mobile terminal correlates the assumptions or test values with the demodulated received signal of the communication information, and the correlation processing consumes the resources of the mobile terminal. If the location of the mobile device is not known at the time of the initial correlation, for example, it could be either location 110 or 120, the search engine will PN-offset._D1And PN-offset_D2You need to search for a window with a PN offset long enough to cover both. However, a smaller search window may be used if the remote terminal is found to be at a particular location 110. Using a smaller search window results in a reduction in the amount of time required for the mobile terminal to correlate with the received signal, and a corresponding reduction in resources.

In a typical CDMA system, the location of the remote terminal with respect to the base station is unknown, so the chip size (W) of the search window is related to the diameter R of the communication cell by the following formula: W = ((2 * R) ) / c) * 2 * chipRate In the chip equation (1) equation (1), c is the speed of light (almost 3 × 10).⁸m / s).

The larger cell size of the communication system corresponds to a potentially larger search window. For example, if the cell has a diameter R of 320 km, the system will be 3.84 x 10 per second.⁶Use the tip rate of the tip. Therefore, the search window W can be as large as: W = ((2 * 320 * 10)³)/3*10⁸)*2*(3.84*10⁶) Chip equation (2) W = 8192 If a chip search was done with a 1/2 chip increment, or 1/2 offset, there would potentially be 16384 offsets in the search window. For a cell diameter of 10 km, 512 1/2 chip offsets with the corresponding smaller search window size can be used. The larger the size of the search window, the more resources of the remote terminal will be consumed during the search. In addition, the size of the search window affects the probability of correlation errors, or false alarms, and a larger search window size results in a higher false alarm rate per window for a false alarm probability per given offset.

If the location of the remote terminal in the cell, i.e. the distance from the base station to the remote terminal, is known, the corresponding smaller search window may be used. This saves resources on the remote terminal and reduces the potential number of false alarms. The present invention utilizes location information to more efficiently adjust the search window size. For example, if the cell diameter is 320 km but the remote unit is known to be within 10 km of the base station, instead of searching for a 16384 window with a PN offset, a window with only 512 PN offsets. All you have to do is search for. Using a smaller search window not only reduces the resources that remote terminals need to devote to the search process, but also reduces the probability of false alarms.

Although this example illustrates correlation processing in a remote or mobile terminal, the same variation of PN-offset depending on the distance between the base station and the mobile terminal is presented in the signal received by the base station. In a CDMA system, mobile terminals generally do not transmit pilot signals, so base stations do not receive correlative pilot signals. However, since the base station still needs to correlate with the signal received from the mobile unit and the mobile terminal transmits its own signal synchronized with the time of the base station, the information about the distance between the mobile terminal and the base station is It can be used to estimate the PN-offset of the signal received at the base station.

As further discussed below, if the distance between the mobile unit and the base station is known, the system determines an estimate of the PN-offset that corresponds to the correlation between the received signal and the local signal. The use of the estimated PN-offset reduces the amount of time and resources required to perform the correlation process and reduces the potential number of false alarms.

FIG. 2 is a block diagram illustrating further details of the PN offset of the signal transmitted by the wireless communication system. In FIG. 2, the pilot signal transmitted by the base station 102 is shown. Generally, the pilot signal is a repeating pseudo-random (PN) code. This code is pseudo-random, i.e. not true random. Because it is a known sequence of repeating "1" and "0". The first bit or chip of the PN code, i.e. the epoch, is specified at point 204. On mobile terminals, a copy 210 of the known PN code is generated locally. The locally generated PN code has the epoch illustrated at point 212.

As described with respect to FIG. 1, as the pilot signal flows from the base station to the mobile terminal, time elapses to cause a delay when the signal is received by the mobile terminal. That is, returning to FIG. 2, due to the distance traveled, the epoch 204 of the pilot signal is not received by the signal 218 at the mobile terminal until a time after time 220. During the correlation, the mobile terminal adjusts its locally generated PN code 210 to match or align with the epoch 220 of the received PN code 218. In the example illustrated in FIG. 2, the locally generated PN code 210 is delayed to match the PN code of the received signal 218. When the mobile terminal 104 is in the first location 110, the amount of delay required for the epochs of the two PN codes 218, 210 to align is the PN-offset._D1And is numbered 136. If the mobile terminal moves to a second location 120, which is farther from the base station, the received PN code 218 is further delayed to epoch 222. The amount of delay required for the two PN codes 218,210 to align at the second location of the mobile unit is the PN-offset._D2And has a reference code of 142. As mobile terminals change locations, the amount of PN-offset required to align the two PN codes changes.

In addition to the PN-offset changing as the mobile terminal changes its location, the frequency of the received signal changes due to the Doppler effect. The Doppler effect changes the frequency of the signal received from the transmitter when the transmitter and receiver are moving relative to each other. When the transmitter and receiver are moving closer to each other, the transmitted frequency is compressed, increasing the frequency of the received signal. When the transmitter and receiver are moving away from each other, the transmitted frequency is expanded and the frequency of the received signal is reduced.

Due to the relative movement between the base station and the mobile station terminal, the communication signal transmitted between the base station and the mobile station is received at a frequency different from the transmitted frequency. Due to frequency ambiguity, receivers are generally configured to receive a number of different frequencies to handle possible Doppler shifts. Since the receiver cannot be configured to receive all possible frequencies, the assumption that the received frequency can be is used to provide an appropriate frequency range for the transmitted signal to be received. .. Information about the relative frequency of the mobile terminal to the base station can improve the choice of assumptions to be used.

FIG. 3 is a block diagram illustrating an embodiment of a mobile terminal and a base station constructed according to the present invention. The mobile terminal 104 includes a transmitter 301 and a receiver 302 for communicating signals with the base station 102. The output of receiver 302 is connected to search engine 304. As described below, the search engine 304 performs a search on the received pilot signal and correlates them. The mobile terminal also includes controller 306 and location engine 308.

The base station 102 includes a transmitter 310 and a receiver 312 for communicating with the mobile terminal 104. The output of receiver 312 is connected to search engine 314, which searches on the received signal. The base station also includes controller 316 and location engine 318.

In one embodiment, the mobile terminal receives a communication signal from base station 102. The location engine 308 receives the navigation information, determines the location, speed, and direction of the mobile terminal 104, and outputs these to the control device 306. Controller 306 determines the reception signal frequency and PN-offset assumptions based on the output of the location engine. The search engine 304 searches for a pilot signal in the communication signal received from the base station using the assumption determined by the control device 306. In one embodiment, the location engine 308 receives navigation information in the form of a signal from a navigation system such as the Global Positioning System (GPS), LORAN-C, or other standard navigation system. In another embodiment, the location engine 308 receives navigation information from the cellular infrastructure. In yet another embodiment, the location engine receives navigation information from both standard navigation systems and cellular infrastructure. In another embodiment, the remote unit 104 receives navigation information signals and sends them to the base station. At the base station, the position, speed, and orientation of the remote unit are determined and returned to the remote unit.

In another embodiment, the base station 102 receives a communication signal from the remote unit 104. The location engine 318 receives the navigation information, determines the location, speed, and direction of the remote unit, and outputs these to the control device 316. Controller 316 determines the reception signal frequency and PN-offset assumptions based on the output of the location engine. The search engine 314 correlates with the received signal from the mobile terminal 102 using the assumptions determined by the controller 316. In one embodiment, the location engine 318 receives navigation information in the form of signals from the mobile terminal 102 and navigation systems such as the Global Positioning System (GPS), LORAN-C, or other standard navigation systems. To do. In yet another embodiment, the location engine 318 receives navigation information from the remote terminal 102 and the cellular infrastructure. In yet another embodiment, the location engine receives navigation information from both the remote terminal 102 and the standard navigation system and cellular infrastructure. In another embodiment, the position, speed, and orientation of the remote unit 104 is determined by the remote unit and transmitted to base station 102.

FIG. 4 is a block diagram illustrating exemplary hardware that can be used to realize various aspects of the invention. In particular, FIG. 4 illustrates the hardware that can be used to account for frequency inaccuracy due to Doppler shift and delay inaccuracy due to PN-offset variations of the received signal. In FIG. 4, receiver 302 receives the communication signal. The output of receiver 302 is connected to multiple paths that should be correlated. Single path 406 is described in detail.

The output of receiver 302 is connected to the mixer 410 to downconvert the received signal along with the reference signal at the appropriate frequency. As discussed, the frequency of the received signal changes due to the Doppler caused by the relative speed between the mobile terminal and the base station, so it is not known what frequency the reference signal should be. Therefore, different reference frequencies (f) based on the selected assumptions₁, f₂, ..., f_n) Is required for multiple mixers 410. The output of the mixer is connected to a second mixer 412, where the locally generated PN code is mixed with the received signal. The locally generated PN code used by the mixer 412 has a different PN-offset based on selected assumptions and corresponds to the distance between the remote terminal and the base station.₁, PN₂, ..., PN_n) Is covered.

Therefore, one set of latent frequencies and one set of latent PN-offsets for the received signal are assumed. The number of combinations with different assumptions can be very large, and many different combinations of assumptions are tried, which consumes a large amount of resources in the mobile terminal. Information about the relative speed of the mobile terminal to the base station allows for better and less selection of assumptions about frequency. In addition, the information about the distance between the mobile terminal and the base station allows for better and less selection of PN-offset assumptions.

FIG. 5 is a flowchart illustrating a technique for determining a search window. The flow starts at block 502. The flow then proceeds to block 504, where the location of the mobile terminal is determined. Next, in block 506, the distance between the mobile terminal and the base station is calculated. Block 508 makes a nominal PN-offset assumption for the received signal. The flow then proceeds to block 510, where a set of PN-offsets, or search windows, used to search for received communication signals is determined. The flow then stops at block 512.

FIG. 6 is a flowchart illustrating a technique for determining frequency assumptions. The flow begins at block 602. At block 604, the speed of the mobile terminal relative to the base station is determined. The flow proceeds to block 606, where frequency assumptions for the received communication signal are estimated based on the speed of the mobile terminal. The flow then proceeds to block 608, where a search for communication signals is performed using estimated frequency assumptions. The flow stops at block 610.

The above description details certain embodiments of the present invention. However, no matter how detailed the above description may be, the invention may be embodied in other particular forms without departing from the spirit or essential properties of the invention. The described embodiments are considered not only as exemplary in all respects, but also as non-limiting. Therefore, the scope of the present invention is shown by the appended claims, not by the above description. All modifications that are synonymous with and conceivable within the scope of the claims should be included in the scope of the invention.

<figref num="1">FIG. 1 is a block diagram illustrating a phase delay of a transmission signal in a wireless communication system.</figref><figref num="2">FIG. 2 is a block diagram illustrating further details of the phase delay of a transmitted signal in a wireless communication system.</figref><figref num="3">FIG. 3 is a block diagram illustrating an embodiment of a mobile terminal and a base station.</figref><figref num="4">FIG. 4 is a block diagram illustrating exemplary hardware that can be used to realize various aspects of the invention.</figref><figref num="5">FIG. 5 is a flowchart illustrating a technique for determining a search window.</figref><figref num="6">FIG. 6 is a flowchart illustrating a technique for determining frequency assumptions.</figref>