Time alignment in a cdma system

SWEDEN (12) PATENT WRITING ds) C2 <11) 521 574 (19) SE ₍₅₁₎

International class ⁷

H04J 13/06, H04B 7/26, 1/707

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PATENT AND REGISTRATION (45) (41) (22) (24) (62) (86) (86) (83)

Patent filed Application widely available The patent application was submitted on expiration date

Application number International filing date

Filing date for European patent application Deposit of microorganism

2003-11-11

1995-09-29

1995-07-27

1994-11-03

1994-11-03 (21) Patent Application Number 9502704-1

Application received as:

Swedish patent application completed international patent application with number PCT / US94 / 12635 converted European patent application with number (30)

1993-11-30 US 159633 (73) (72) (74) (54) (56) (57)

PATENT OWNER Motorola Inc., Schaumburg Ill US

INVENTOR Eugene J Bruckert, Arlington Heights Ill US, Richard A Sunday, Lake Zurich Ill US

OMBUD Ehrner &amp; Delmar Patentbyrå AB

NAME Method and apparatus for timing signals for reception in a communication system with code-shared multi-user access

CALLED PUBLICATIONS:

US A 5,257,404

SUMMARY: .....

A coherent return channel (120), a cnrp-ror-snip riding function, crtgonal spreading functions, and a timing of all traffic signals are implemented so that the main signal arrives at each channel to a basinome. your. cclccsj. sv vs-snci — ä for 5Ω-ms in upotemple. Because of this, the trtogonality is maintained among all channels and when demodulated all channels except the interesting channel give a cross correlation soot is essentially zero with respect to the remaining signals.

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The numbers in brackets indicate international identification code, INID code. Letters in clamps indicate international document code.

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SUMMARY

A coherent return channel (120), a chip-by-chip spread function, orthogonal spread functions and a timing of all traffic signals are implemented such that the main signal on each channel arrives at a base station within a chip portion of each other in accordance with the invention. By this, the orthogonality is maintained among all channels and when demodulated all channels except the channel of interest give a cross correlation which is essentially zero with respect to the remaining signals.

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Field of the Invention

The present invention relates generally to communication systems, and more particularly to timing of signals for reception in communication systems with code-shared multi-user access.

Background of the invention

In multi-user code-sharing (CDMA) communication systems, communication between a base station and a subscriber unit is achieved by spreading each transmitted signal over the communication channel's frequency band with a unique user spread code. As a result, transmitted signals are within the same frequency band on the communication channel and are only separated by the unique user spread codes. These unique user spread codes are preferably orthogonal to each other so that the cross-correlation between the spread codes is virtually zero.

In particular, transmitted signals can be recovered from the communication channel by gathering a signal representative of the sum of signals on the communication channel with a user spread code related to the particular transmitted signal to be recovered from the communication channel. Furthermore, when the user spread codes are orthogonal to each other, the received signal can be correlated with a particular user spread code so that only the desired signal related to the particular spread code is amplified while the other signals for all the other users are significantly diminished.

In order to maintain the orthogonality of all channels, the channels must be essentially timed chip by chip. For front channel transmission (from base station to subscriber unit), this timing is achieved

521 574 • · «fit easily via a synchronized process for combining the traffic channels with each other in each base station. However, timing of return channel signals (from the subscriber units to a certain base station) is not as simple due to the temporal randomness of the subscriber units' broadcasts. Attempts have been made to synchronize the return channel signals in a base station, but such attempts require additional circuits in the base station, which in turn leads to both increased complexity and an increased cost for the base station.

Thus, there is a need for a simple and cost-effective method and a corresponding device for timing signals for reception in a CDMA communication system.

Brief description of the drawings

Fig. 1 generally shows, in block diagram form, a communication system according to the invention.

Fig. 2 generally shows a front channel frame having an advance / delay bit according to the invention.

Fig. 3 generally shows, in block diagram form, an alternative embodiment of a transmitter which can be used in accordance with the invention.

Detailed description of a preferred embodiment

A coherent return channel, a chip-by-chip spread function, orthogonal spread functions, and timing of all traffic channels are implemented such that the main signal on each channel arrives at a base station within a portion of a chip of each other in accordance with the invention. This maintains the orthogonality of all channels and all channels except the interesting channel, after demodulation, provides a cross-correlation which is essentially zero with respect to the remaining signals. In this way, an extra sensitivity of at least 2 dB can be achieved in typical CDMA communication systems, and as much as 10 dB in a personal communication system (PCS) environment, where it is less

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3.

it is likely that spreading effects due to delay occur.

Fig. 1 generally shows, in block diagram form, a communication system according to the invention. In the preferred embodiment, the communication system of Fig. 1 is the coherent communication system which is essentially shown and described in patent application No. 08/031258, entitled Method and Apparatus for Coherent Communication in a Spread Spectrum Communication System, filed March 11, 1993, by inventor Fuyun Ling and incorporated herein by reference. Fig. 1 also shows a comparator 169, a modulator 170, a demodulator 178 and a clock 151.

The comparator 169 has as an input a clock signal 149 which is output from the clock 151, and a power estimate signal 148 which is output from a power estimator 146. In the preferred embodiment, the power estimator 146 utilizes a summation and squaring technique to perform power estimation well known in the art. During operation, a demodulator 122 outputs outputs 148 and 149 (and so does demodulator 123, with its corresponding clock signal 153 and power estimate signal 155) to comparator 169, where the signal with the greatest estimated power is determined. In the preferred embodiment, four demodulators are used to receive a single transmission from a subscriber unit. Each demodulator demodulates a delayed beam in the subscriber unit transmission, based on an assignment determined by the delayed beam's energy. Although not shown separately, each of the four demodulators can be switched between a plurality of antennas connected to a base station. The clock signal from the demodulator having the highest estimated power is then used for comparison, in comparator 169, of the time at which the delayed signal was received with a reference value to determine a time position for each signal. Two rays having substantially the same delay will be combined in comparator 169 prior to comparison with the reference value. Further

521 574, in the same way, an average of the arrival times of the multiple (four) delayed rays representative of the signal can be used for comparison with the reference value in comparator 169.

In the preferred embodiment, the reference value may be an (absolute) expected arrival time of the signal (i.e., a single subscriber unit transmission) or a value related to the arrival time of signals relative to each other (ie, a group of subscriber units transmissions). For example, a value related to the arrival time of the signals in relation to each other could be an average of the arrival times of all signals (and / or their delayed rays), the most recent arrival time of the arrival times of all signals, etc. As will be appreciated by one of ordinary skill in the art. there are many characteristics / combinations of the signals / rays for the determination of the reference value.

Once the signal state has been determined, comparator 169 generates an adaptation signal 171 which is transmitted to a subscriber unit, such as a subscriber unit which is made up of, for example, blocks 100 and 116. The subscriber unit receives the adaptation signal, sets the clock based on the adaptation signal and transmits information to a base station. utilization of the set clock. In this way, the technique according to the invention is utilized to either delay or delay a subscriber unit broadcast from the base station's perspective.

In the preferred embodiment, the function of a modulator 170 is substantially the same as that of modulator 117. An adaptation signal 171 is input into modulator 170 and so also occurs with a signal 172 (substantially equivalent to signal 114). The modulator 170 then transmits, among other things, the adaptation signal 171 to the corresponding subscriber unit (and other adaptation signals to other corresponding subscriber units) so that any subsequent signals transmitted by said

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In »» several subscriber units are received by the base station substantially timed.

In the preferred embodiment, the matching signal 171 can be generated in many ways. First, it can be generated as a message. In IS 95, published by the Telecommunications Industry Association, 2001 Pennsylvania Avenue NW, Washington, DC, there is a kit titled Ordered Messages that allows a manufacturer of the equipment to create customer messages. For the adaptation signal 171 in accordance with the invention, the message may look like the message in Table 1 below:

TABLE 1

Personsökkanalordning

No

Up Traffic Channel Order

Yes

order code,

ORDER (binary)

011111

Order Quality Code ORDQ (binary) snnnnnnn

ACTION TIME can be specified

ORDQ

No

Additional fields second

No

Name / funk.

Timing scheme where nnnnnnn is a time value field, where the value of the change in time adjustment (in nanoseconds) exists, and s is a polarity change field, in which the polarity of the change (advance / delay) is specified. The message would be transmitted on the forward traffic channel with an order code (eg) of 011111 and given the title Timing Order.

A second embodiment would incorporate a pre-delay / delay bit inserted into a front channel frame such as that shown in Figure 2. The frame would be a modified version of the front channel frame as defined in the standard IS 95. In bit position 1, when a message mode (MM) is 0, a subscriber unit would know that prior / delay is required. In bit position 2, a pre-delay / delay (AR) bit would indicate what action to take; if AR = 1 then the timing is an earlier one and if AR = 0 then the timing is a

521 574 i »• 6 delay. Usually, the timing change is a small portion of a chip (e.g. less than 1/10 of the period for that chip).

For each subscriber unit in the communication system, there is one unique, unique distribution code. When a base station transmits an adaptation signal 171 to each subscriber unit, each subscriber unit will delay / delay its transmission so that each subsequent transmission will be timed when received and demodulated by the base station.

Fig. 3 generally shows in block diagram form, an alternative embodiment of a transmitter which can be used in accordance with the invention. In this embodiment, a transmitter portion 116 comprises a modulator operating with quadrature phase shift technology (QPSK), which is well known in the art, and which is connected to a linear power amplifier (LPA) 318). The transmitter portion 116 of FIG. 3 can also be implemented using a π / 4-QPSK modulator if a circuit 306 rotates the phase with π / 4 radians each chip. One skilled in the art would also recognize that transmitter portion 116 can be easily adapted for offset QPSK modulation implementation.

As is well known to one of ordinary skill in the art, CDMA communication systems utilize soft handoff. In a soft handoff situation, a subscriber unit receives (synchronized) transmissions from more than one base station. A subscriber unit receiving the adaptation signal transmitted in accordance with the invention, in a preferred embodiment, would receive multiple transmissions but only follow the pre-delay / delay command contained in one of the transmissions (e.g., the transmission having the highest power seen from subscriber unit). In an alternative embodiment, a subscriber unit could be instructed by a base station to follow a particular base station's timing commands of the received base stations.

The timing according to the invention is applicable to a typical microcell system shown in

521 574 »» »» »Fig. 4, where a control unit 400 connects base stations 409, 412 in microcells 403 and 406, respectively. Figure 4 also shows a cell 415 in a cellular system having a base station 418 which is also connected to the controller 400 (the link is not shown). In typical microcellular systems, cell 403, 406 is considerably smaller than cell 415 in a traditional cellular system, as can be seen in Figure 4.

As a result, the delay / delay is usually not a concern in microcell systems, since individual subscriber unit transfers in a microcell 403 or 406 arrive essentially timed because the cell is small. Adjacent microcells 403, 406 still exhibit mutual interference, as occurs in neighboring cells in cellular systems. Accordingly, the value related to the mutual arrival times of signals can be used to set up a whole group of subscriber unit transfers (within a given microcell) using a common time, so that the principle of orthogonality can be utilized in a winning manner between adjacent microcells. For example, if orthogonal spreading codes are implemented between microcells as compared to orthogonal spreading codes implemented between subscriber units), a setting to broadly match an entire group of subscriber unit transfers (within a particular microcell) with a whole group of subscriber unit transfers (within an adjacent microcell) would the orthogonality gains between microcells that can be seen between subscriber units in the above-described preferred embodiment. In this alternative embodiment, comparator 169, for each receiver demodulating a single subscriber unit transmission, would have an output signal (not shown) that would be input to controller 400. Controller 400 would determine an adaptation group time signal, giving command to base stations 409, 412 to ensure that each subscriber unit in the group is set accordingly. By setting the whole group into a microcell 403, 406, the ortho521 574: 6 · principle of gonality can be utilized advantageously between adjacent microcells, so that any cross-correlation between the microcells is essentially 0. An example of an application of group timely relay / delay would be to advance / delay a subscriber group in a lightly loaded microcell in order for a heavily loaded microcell to benefit from it.

Although the invention has been shown and described with reference to a particular embodiment, those skilled in the art will readily recognize that various changes in shape and details may be made without departing from the scope of the invention.

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