US 20050128978 A1
A method of compressed mode communications permits evaluation of one communication system while communicating in another communication system. User equipment devices (108, 110) are assigned to different portions of a frame during compressed mode.
1. A method of operating a user equipment to measure and synchronize with one radio communication system while communicating with an other radio communication system, at least the other communication system being a framed communication system, the method comprising the steps of:
communicating with the other communication system in a first portion of a frame;
evaluating the first communication system during a second portion of the frame; and
changing the portion of the frame where the communicating and evaluating occur over a sequence of compressed frames.
The present invention pertains to framed signaling, and more particularly to a method and apparatus utilizing compressed mode operation for framed signals.
Third generation wireless mobile user equipment will support dual radio access technology, such as by supporting communication over 3G (third generation) systems, such as wideband code division multiple access (WCDMA) systems, and 2G systems, such as Global Systems for Mobile communications (GSM) systems. Such user equipment will be required to acquire and maintain knowledge of multiple radio frequency domains with regard to signal strength of serving and adjacent cells, interference, and synchronization. When such user equipment is operating in idle mode, which is the mode where the user equipment is not engaged in dedicated communication with a serving cell, the implementation of such procedures is straightforward.
However, where the user equipment is engaged in dedicated communication on a serving cell of one system, requiring that it both receive and transmit signals, there may be a lack of time available during which measurements or synchronization of the other systems supported by the equipment can take place. For example, if user equipment is engaged in dedicated communication with a serving cell on the Universal Terrestrial Radio Access (UTRA) domain using frequency division duplex (FDD), the user equipment must transmit during each available frame period. This limits the time available for performing measuring and synchronization with a cell of a GSM system.
To overcome this problem, third generation partnership project (3GPP) specification section 25.212 specifies “compressed mode” operation, during which the mobile user equipment, or the network, may transmit during only a portion of a frame in order to allow measurement and/or synchronization during the other portion of the frame. However, this specification requires transmissions to be performed using a smaller spreading factor, thereby necessitating a 3 dB greater transmission power to achieve a suitable bit-error rate (BER). The specified method thus severely impacts the capacity of the cell, as the number of devices operating in compressed mode will be limited by the increased power requirements.
The 3GPP specification describes three methods for reducing the signal length to create a transmission gap for compressed mode operation. Puncturing, by which data redundancy is removed for a compressed frame to allow transmission within a shorter time period. This technique allows more data to be transmitted at the expense of error correction capability. A second technique is spreading factor reduction, by which the spreading factor is reduced by a factor of 2, thereby requiring half the time to transmit a given amount of data. However, such a reduction is at the expense of processing gain, which is applicable to both the uplink and the downlink. A third method of reducing the signal length is higher layer scheduling.
What is needed is an improved compressed mode communication.
The various aspects, features and advantages of the present invention will become more fully apparent from the following Detailed Description with the accompanying drawings described below.
A complementary compressed mode method and apparatus facilitate evaluation of one communication system while communicating in another communication system. User equipment devices (108, 110) are assigned to different portions of a frame during compressed mode operation.
A cellular communication system 100 (
The user equipment 108 includes transceiver 204 (
In operation, as the user equipment 108, 110 moves through the system, hand-off will occur according to ordinary operating techniques, which are well known in the art. For multi-mode user equipment, such as those operating over a plurality of different communication air interfaces, the user equipment 108, 110 will be required to acquire and maintain knowledge of multiple radio frequency domains, and may for example maintain knowledge of signal strength of serving and adjacent cells, interference information, and synchronization information, as is known to those of ordinary skill in the art.
While the user equipment 108, 110 establishes a dedicated communication link with a base in the first communication system 101, which is illustrated as a UTRA system, the user equipment will at least occasionally be required to evaluate system 104, a GSM system. This may for example occur when the user equipment 108 moves to the edge of cell 101′, 101″ adjacent cell 103′. In the illustrated embodiment, cell 103′ covers an area not served by communication system 102, and thus user equipment 108 will need to be handed off from base station 200 to base station 220. In order to support the measurement and synchronization processes that user equipment 108 must perform while engaged in communications with base station 200 of cell 101′, at least the uplink communications between the user equipment 108 and base station 200 are made in compressed mode.
More particularly, the user equipment 108 (
Thus, in compressed mode, a transmission gap is created during which the user equipment may perform measurements without encountering a scheduling conflict. A scheduling conflict would otherwise occur where the user equipment attempts to perform two tasks simultaneously with a single transceiver path. Additionally, compressed mode occurs without subjecting the system to prohibitively high levels of self-interference, as in the case of inter-mode measurements that may occur at the same time in the same or a close frequency band.
In normal mode, the CDMA signals from user equipment 108, 110 are separated from one another by a channel identification code on the uplink. The signals in the downlink are also separated by a channel identification code. During compressed mode, the channel identification code (e.g., an orthogonal code in CDMA) still isolates the signals, but the information rate is effectively “sped up” by a factor of 2 in response to the spreading factor being reduced by ˝. It is necessary to increase uplink power for the user equipment 108, 110 in compressed mode to compensate for the loss of processing gain due to the lower spreading factor. A significant problem encountered with a system operating according to
As used herein, in a “compressed mode pattern,” a certain number of frames having transmission gaps are followed by a certain number of frames that do not have transmission gaps, and this pattern repeats with a periodicity of a certain number of frames. Compressed mode pattern thus refers to: the number of time slots during which transmission occurs within the period of a given frame; the number of time slots during which compression does not occur within the period of a given frame; the number of compressed frames in which compressed transmissions occur during time slots of a given frame; and the number of non-compressed frames in which compressed transmission does not occur during the time slots of a given frame.
An example of a transmission pattern is illustrated in
A significantly improved system for compressed mode operation is illustrated in
Although the first portion and the second portion may be allocated from many different groups of slots, one pattern envisioned is to divide the frame into 15 slots. The first portion comprises 7 slots that are allocated to a plurality of devices separated by orthogonal codes. The second portion comprises the last 7 slots that are allocated to another group of devices, also separated by orthogonal codes. The third portion is a separation slot in the middle of a frame. In one embodiment, it is envisioned that the devices allocated to the first portion will have different orthogonal codes than the devices in the second portion. The slots are preferably of equal length.
To examine the effects of amplitude variations based on the type of pattern (on/off sequence) selected, a simulation was used to generate various compressed mode patterns in terms of the radio frequency (RF) envelope shape, and then a Fourier transform was used to determine the spectral properties of the envelope. The 7-1-7 slot compressed mode pattern was found to have favorable spectral characteristics when compared to other patterns when user equipment were paired.
In particular, Fourier analysis was used to compute the spectrum of the RF envelope having the maximum allowable rise time and a decay time of 25 μs. The following simulation used compressed mode patterns, each of which has a repetition period of 12 frames, i.e. 2 compressed frames followed by 10 uncompressed frames, which pattern was repeated. The inventors found a significant degree of cancellation of spectral components under 100 Hz (frequency number approximately 125) for the 7-1-7 pattern. While there are many other combinations of patterns that may be compared and utilized with the invention, the 7-1-7 pattern using a repetition period of 12 frames resulted in lower uplink interference.
The user equipment 108 will now be described in greater detail with reference to
The MAC layer 506 maps logical channels from the RLC 508 to transport channels in the physical layer. The RLC 508 controls the transmission link over the radio medium.
The RRC layer 510 controls radio operation of the user equipment 208 (or 210). RRC layer 510 includes a control message recognizer 514, which outputs downlink messages to the control message parser 516. Compressed mode control messages are input to the uplink compressed mode controller 518. The compressed mode controller generates message acknowledgements, which are input to the uplink user data path for communication to the base station. The uplink compressed mode controller also generates compressed mode control information, pattern assignment information, and resource assignment and measurement scheduling, which is determined as described in greater detail hereinbelow. The physical layer includes an uplink compressed mode pattern and assignment manager 520 responsive to the compressed mode pattern received from the uplink compressed mode controller 518. An uplink transmission controller 522 communicates via the radio frequency transceiver 204 under the control of resource assignments received from the uplink compressed mode controller 518. The physical layer further includes a measurement acquisition unit 524, responsive to the measurement schedule from the uplink compressed mode controller 518 for acquiring measurements and communicating the measurements to the measurement processor 526 in the radio resource controller 510.
The RCC layer 610 controls radio resources. The RCC includes an uplink compressed mode controller 614, which receives downlink signal data and generates uplink signal data. The compressed mode controller communicates with the uplink traffic scheduler 616. Additionally, the uplink compressed mode controller communicates the measurement schedule to the measurement acquisition unit 612. A measurement processor 618 receives the measurements from the measurement acquisition unit 612.
The operation of the system will now be described with reference to
An alternate embodiment is illustrated in
Yet another alternate embodiment for assigning compressed mode operation is illustrated in
It is envisioned that the deterministic value may be any value known to the user equipment and the base station, and may for example be a particular bit of the subscriber equipment IMEI, such as the last bit of the subscriber equipment IMEI. An alternative deterministic value could be a predetermined bit of a signal communicated from the user equipment to the network, such as a bit stored in memory in the user equipment. Another alternative can be a random or pseudo-random number generated by circuitry in the user equipment and known to base station.
In step 1206, the controller in the user equipment and the base station determines whether the deterministic bit is a 1 or a 0. If the bit is a 0, then the communication in compressed mode will be in portion 1 for the initial frame. If the bit is a 1, the communications in the compressed mode will use portion 2 for the initial frame, as indicated in step 1208. The controller waits for the next frame in step 1214. If the next frame is after the last frame of the compressed mode sequence, as determined in step 1216, the compressed mode communication ends. If the frame is not after the last frame of the compressed mode sequence, the controller identifies the deterministic value for the next frame in step 1218, and returns to decision step 1206. This process will be repeated for the compressed frames in the compression pattern.
With complementary compressed mode, the uplinks are still processed by reducing their spreading factor by ˝, except that instead of being isolated from one another by orthogonal codes, they are now temporarily isolated in a manner of a slotted physical access mechanism. Additionally, compressed mode operation can be assigned to pairs of user equipment devices, each with a complementary pattern.
The present invention has significant technically and commercially desirable attributes. It reduces the peak-to-peak amplitude variations arriving at the Node-B receiver from a given pair of user equipments assigned to symmetrical compressed mode. This results in lower self-interference on the uplink, and therefore greater cell capacity. Additionally, a timeslot pattern and period can be selected that demonstrates surprising spectral characteristics for the RF envelope to be optimized.
While the present inventions have been described in a manner that enables those of ordinary skill in the art to make and use the inventions, it will be understood and appreciated that there are many equivalents to the exemplary embodiments disclosed herein and that modifications and variations may be made without departing from the scope and spirit of the inventions, which are to be limited not by the exemplary embodiments but by the appended claims.