Neighbor-assisted handover in mobile communications systems

NEIGHBOR-ASSISTED HANDOVER IN MOBILE COMMUNICATIONS SYSTEMS

BACKGROUND OF THE INVENTION Field of the Invention [0002] The present invention relates generally to wireless communication systems, and more particularly, to handover technology.

The cellular system connects a user terminal such as a cellular phone to the cellular system by utilizing a plurality of base stations. Each user terminal initially communicates with the base station to exchange information with the system. However, when the user terminal physically moves or the user terminal experiences congestion while the current base station is servicing another user terminal, the user terminal must be handed over to other base stations subsequently.

In an advanced cellular system, several aspects of a communication link between a base station and a user terminal vary depending on the location of the user terminal. Examples of location-dependent parameters include modulation level and coding rate, transmit power, and timing advance for uplink transmission.

In the normal case, parameters appropriate for a particular user terminal should be determined by a process that includes probing the channel condition, reporting the result, and facilitating signaling/negotiation of values between the base station and the user terminal. Unfortunately, this process typically utilizes a fraction of the channel capacity available to carry data traffic. Furthermore, in a packet data system, terminals typically use the system in a burst manner rather than continuously. As a result, the user terminal can move between transmissions or go into power saving mode and need to re-establish the appropriate link parameters on a frequency basis, further reducing the data capacity or increasing the latency of the system.

In addition, the performance of handoff of a user terminal from one base station to another can potentially degrade the quality of service (including bit rate, latency, voice quality) or lead to dropping a call on the so-called neighbor list. dependent If the size of the neighbor list changes, a larger neighbor list may increase the measurement volume required for handoff. This increases latency and/or shortens battery life for the user terminal. In addition, the neighbor list provides inappropriate and outdated information during startup or emergency from a power saving (eg, dormant) mode, which typically occurs frequently in packet data systems.

Like reference numerals throughout the several drawings refer to identical or functionally similar elements, and the accompanying drawings, which are incorporated in and form a part of the specification together with the following detailed description, further illustrate various embodiments in accordance with the invention and It serves to explain all of the various principles and advantages.

1 illustrates a user terminal communicating with a base station according to an embodiment of the present invention.

2 illustrates a block diagram of a user terminal according to an embodiment of the present invention.

3 illustrates a user terminal exchanging cellular system information with a second user terminal in a cellular system according to an embodiment of the present invention.

4 illustrates a method of a user terminal for obtaining cellular system information including cellular system parameters from a user terminal according to an embodiment of the present invention.

5 illustrates a cellular system utilizing a seed terminal according to an embodiment of the present invention.

Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some components in the drawings may be exaggerated relative to other components to help improve understanding of various embodiments of the present invention. In addition, commonly known components useful or necessary in a commercially suitable embodiment are not shown in order to less obscure the view of various embodiments of the present invention.

Generally speaking, in accordance with various embodiments, methods and systems are provided for exchanging cellular system information from one user terminal, such as a cellular phone, directly to another user terminal. The information is provided in a second form directly from the first user terminal, so that the second user terminal can determine various channel operating conditions, parameters, and lists of neighboring base stations without having to utilize the bandwidth of the channel to communicate with the base station to determine this information. exchanged at the user terminal. Instead, the user terminals may each include a transceiver that communicates with other adjacent user terminals via, for example, Bluetooth, or a wireless local area network ("WLAN").

By directly obtaining information from neighboring user terminals, accurate and timely cellular system information is obtained, for example, regarding operating conditions, parameters, and lists of neighboring base stations for handing over the call. Moreover, the burden on the cellular system resource for adapting the terminal parameters is substantially reduced.

1 illustrates a user terminal 100 communicating with a base station 105 according to an embodiment of the present invention. As described above, the user terminal 100 includes, for example, a cellular phone. The user terminal 100 is communicating with the base station 105 when, for example, a call is made through the user terminal 100 . When a call is made, data is transmitted between the user terminal 100 and the base station 105 . Data includes information from various services such as data file delivery, voice services, video services, games, and the like. The base station 105 is also in communication with the core network 110 . The core network 110 may be, for example, a third generation (3G) network element, a fourth generation (4G) element, an 802.20 element, or a short range such as a Bluetooth or wireless local area network (WLAN, eg, IEEE 802.11). other current networks utilizing next-generation handsets with short-range capabilities. Data is transmitted from the base station 105 via the core network 110 and to a final destination, which may be another base station in communication with another user terminal or a fixed terminal.

The user terminal 100 may be in communication with the base station 105 when physically located within the cell of the base station 105 , that is, a service area. However, there are multiple base stations with overlapping cell coverage within the same geographic area. Thus, a call made with the user terminal 100 may often be handled by either the base station 105 or another base station within the same geographic area. Each base station has a limited amount of radio bandwidth to communicate with the user terminal. Thus, the base station 105 can service multiple calls at a time only until the radio bandwidth limit is reached and the service of current calls is adversely affected. As the user terminal moves near the edge of the cell, the call is handed off to another base station 105 that can better service the call. To determine the base station 105 to hand off the call to, the user terminal 100 may utilize a "neighbor list", ie a list of neighboring base stations, that can service the call.

2 illustrates a block diagram of a user terminal 100 according to an embodiment of the present invention. As illustrated, the user terminal 100 includes a processor 150 , a memory 155 , a timer 160 , a battery 165 , a detection element 167 , a collection element 169 , and a communication element. (170). The communication element includes one or more transceivers having a transmitter element and a receiver element and provides the user terminal 100 with the ability to communicate wirelessly with the base station 105 and other user terminals. The processor 150 may be in communication with the memory 155 , the timer 160 , the battery 165 , and the communication element 170 . Memory 155 may include, for example, a flash memory device. The timer 160 may include a mechanical timing device. Alternatively, the timer 160 may include a software program executed by the processor 150 . The user terminal 100 may include a battery 165 to provide power to the processor 150 . In this embodiment, the communication element 170 is capable of Bluetooth and/or WLAN communication.

When communicating with the base station 105, the user terminal 100 needs to utilize various link parameters or other system parameters. Determining appropriate parameters for user terminal 100 by a process comprising probing channel conditions, reporting results to base station 105 and performing signaling/negotiation of values between base station 105 and user terminal 100 Instead, the user terminal 100 communicates, for example, via Bluetooth or WLAN, with other nearby user terminals that have already performed a similar test to determine the parameter or have obtained the parameter from another user terminal, thereby acquire many or all of them.

User terminal 100 gathers information from neighboring user terminals to help adapt link parameters (or other system parameters) and more generally learn more about the system. The detection element 167 detects the second user terminal of the wireless system having the wireless system information, and the collection element 169 collects the radio system parameters in a timely manner from the second user terminal. The collecting element 169 may also be constructed and arranged to collect timely wireless system parameters prior to the user terminal communicating with the base station 105 . Although the detection element 167 and the collection element 169 are shown in FIG. 2 as being external to the processor 150 , in various embodiments of the invention, one or more of the detection element and collection element is the processor 150 . can be implemented in

Accordingly, the user terminal 100 obtains as much cellular system information as possible from the neighboring user terminals 100 so that the amount of signaling overhead of the cellular system is reduced. Additionally, the power consumption of the user terminal 100 is reduced, making the life of the battery 165 of the user terminal 100 longer. However, there are instances in which individual battery resources may be adequately utilized for overall system benefit. In many cases, reducing signaling, or generally reducing the use of over-the-air (OTA) cellular resources, will reduce latency and latency for the user terminal 100 .

3 illustrates a user terminal 200 exchanging cellular system information with a second user terminal 205 in a cellular system 207 according to an embodiment of the present invention. As shown, the user terminal 200 is communicating with the base station 210 . The user terminal 200 may be similar to or the same as the user terminal 100 shown in FIG. 2 . The base station 210 is in communication with the core network 215 . Accordingly, when a call is made with the user terminal 200 , data is transmitted from the user terminal 200 to the base station 210 , and then the base station transmits the data to the core network 215 . The base station 210 provides a cellular service within the cell 220 . Outside the range of the cell 200 , the user terminal 200 must be handed off to another base station that can provide a better or more reliable service to the user terminal 200 .

As illustrated, the user terminal 205 is initially located outside of the cell 220 . Prior to entering the cell 220 , the user terminal 205 has minimal knowledge of the base station 210 , including the various communication protocols required to communicate with the base station 210 . These protocols may be location-dependent parameters such as modulation level and coding rate, transmit power, timing advance for uplink transmission, and/or identity of neighboring base stations.

Accordingly, when the user terminal 205 enters the cell 220 , the user terminal 205 needs to obtain parameters. As described above, the user terminal 205 obtains parameters from other user terminals, such as the user terminal designated by reference numeral 200, which already exists in the cell 220 .

The exchange of cellular system information between the user terminals 200 and 205 reduces the use of cellular resources, so that, for example, the bandwidth of the base station 210 is not excessively used by the user terminal 205 to determine system parameters. . The user terminal 200 provides the user terminal 205 with handoff parameters (eg, a list of neighboring base stations), random access generation parameters to avoid random access channel ("RACH") collisions, and location information. . Downlink data is relayed from a plurality of nearby user terminals that are combined at the target, and the shared location information is used to assist in the determination of various parameters, resulting in faster reception and fewer communication errors. The user terminal 200 shares broadcast data to reduce radio subscription requests and grants. For example, if the user terminal 200 is a subscriber of a broadcasting radio program, the user terminal 200, for example, after receiving data on the broadcasting program from the user terminal 200, the user terminal 205 send to

User terminals 200 may share system information that is transmitted on an irregular basis, such as only once per superframe (eg, time division duplexing ("TDD") splits, cyclic prefix lengths, etc.). The user terminal 200 provides the user terminal 205 with current system performance parameters such as average loading, average latency, and average received carrier-to-co-channel interference ("C/I") ratio. Such information can help a multi-mode and/or multi-band user terminal to select an appropriate network that meets its user requirements.

Referring to FIG. 3 , the user terminal 200 may be a currently or recently activated user terminal. The user terminal 200, along with most other user terminals, may have built-in WLAN or Bluetooth capabilities so that it can be used to access WLAN hotspots. The cellular system 207 may utilize TDD and orthogonal frequency division multiplexing ("OFDM") transmission. Consequently, accurate uplink timing advance is important for proper operation of the system (eg, to avoid inter-cell interference), and the initial advance procedure involves significant overhead. The user terminal 200 is located, for example, 1.5Km from the base station 210, and may have adapted parameters for proper communication with the base station 210 including, for example, a timing advance setting of 5 μs. .

4 illustrates a method for the user terminal 205 to obtain cellular system information including cellular system parameters from the user terminal 200 according to an embodiment of the present invention. First, in step 300 , the user terminal 205 is powered when in the vicinity of the user terminal 200 . Alternatively, the user terminal 205 wakes up from a sleep mode. The user terminal 205 can access the cellular system 207 to adapt the parameters. However, prior to communicating with the base station 220 , the user terminal 205 may, in step 305 , present any cellular system information regarding the cellular system 207 and/or any within a predetermined communication range having appropriate user terminal parameter values. It searches and determines whether there is an adjacent user terminal. This may be done, for example, in step 310 by sending the request at low power on the WLAN channel so that only adjacent user terminals receive the request. This low power level may be a different (and lower) power level that may be used for WLAN communication with a WLAN access point ("AP"). Alternatively, the communication method may be Bluetooth or other type of direct user terminal-to-user terminal communication.

Alternatively, the user terminal 200 and the additional user terminal (not shown) automatically transmit a low-power beacon signal on the WLAN channel by any user terminal having timely information to share cellular system information with other user terminals. It can be configured to inform that it has Since the minimum packet size of a WLAN system can carry a significant amount of information, parameter values can be included in the beacon signal.

After the user terminal 205 determines that the user terminal 200 is nearby and has cellular system information in a timely manner, in step 315 , including a number of initial system parameters and/or neighbor lists from the user terminal 200 Collects cellular system information. For example, the user terminal 205 collects the cell ID and channel number. This information helps the user terminal 205 to accelerate the initial cell search procedure. This provides a means to verify whether the information from the user terminal 200 is actually available by the user terminal 205 . After the user terminal 205 determines which cell to join and the corresponding cell ID, it may check to determine whether the information from the user terminal 200 is actually from the same cell 220 . After the cellular system information is collected, the cellular system information stored in the memory of the user terminal 205 is updated or initialized to the cellular system information in step 320 . When the neighbor list is exchanged between the user terminals 200 and 205, the user terminal 205 performs measurement or the like with at least one base station of the communicated neighbor list.

Sharing of cellular system information between user terminals 200 and 205 is very beneficial. Neighbor list or need to handoff is location-dependent, so neighbor list information from nearby user terminal 200 is available by user terminal 205 .

The user terminal-to-user terminal communication link being utilized will further drive the use of such proximity information. If the typical communication range of the technology used for user terminal-to-user terminal communication is too large, the search may This can be done by reducing the communication range using technology with reduced power. For example, given the shorter range of Bluetooth when compared to WiFi, it may be subject to such proximity information much more when obtained over a Bluetooth link than when obtained over WiFi. Therefore, GPS-assisted location information can also be helpful.

Although only user terminals 200 and 205 are shown in FIG. 3 , additional user terminals may also be utilized. Cellular system information from recent measurement report information from a plurality of user terminals is utilized to tune or verify measurements. The measurement report is practically used to filter the neighbor list of the base station making measurements for the user terminal moving to a new cell, powered on or waking up from dormant mode.

Another parameter that the user terminal 205 collects for the user terminal 200 is a timing advance value. The initial timing advance value for the user terminal 205 is based on a corresponding value used by the user terminal 200 . This can improve the performance of the random access channel of the system and reduce the number of bits required to perform any further adjustment of the timing advance.

Initial power control, modulation and coding scheme ("MCS"), path loss, transmit power ("Tx power"), downlink channel-to-interference ("C/(I+N)") ratio, used on downlink Additional parameters may be exchanged, including those that help determine the modulation and coding scheme to be used, and the modulation and coding scheme to be used on the uplink. Other parameters exchanged include those that determine the initial multi-antenna technology to utilize. Some parameters are exchanged to assist the user terminal 205 in determining the type of performance expected, such as average cell loading, average latency, average bit rate based on experience, and the like.

Depending on the type of relay used, pre-information may be exchanged to perform high-speed/efficient relay. For example, the closest relays, routing paths, etc. may be exchanged. For the hierarchical routing concept, it can be a way to join the system in ad-hoc mode without having to wait for the next routing tree update. This reduces latency because the user terminal 205 joins the system and immediately achieves a high bit rate.

In addition, the user terminal 200 may advertise that it can be used as an uplink relay for a specific traffic class and for a specific time duration. The user terminal 200 may have higher transmit power performance than the portable user terminal. The cellular system 207 may penalize the user terminal 205 by providing incentives such as cost credits, airtime credits, etc. to the user terminal 200, for example, by doubling the airtime minutes. can

Some of the above-mentioned parameters, such as C/(N+1) and cell ID, may be obtained by passively monitoring the downlink of the cellular system 207, in which case using any additional usage of cellular system resources. it won't be However, obtaining such information from the adjacent user terminal 200 may be more efficient in terms of time and power consumption.

User terminal 200 and user terminal 205 each use a timer (eg, as shown in FIG. 2 above) or other means for determining whether these parameter values are still valid (ie, timely). and use this to determine whether to transmit information to a neighboring user terminal. Also, after the user terminal 205 receives the cellular system information from the user terminal 200 , the user terminal 205 may determine whether the received cellular system information is correct. A way to do this is to monitor multiple user terminals. Another method is to obtain this information directly by performing some system measurement (eg downlink C/(N+1)) and comparing it with what the neighboring user terminals are reporting. Additionally, the user terminal transmission includes relative time information (ie relative to the current transmission time) when the user terminal specific parameter values are updated, such as the parameters were adapted in a certain number of frames prior to the current transmission. Then, the user terminal 200 monitoring the plurality of neighboring user terminal transmissions may select a parameter considered to be the most recent among the plurality of neighboring user terminal transmissions.

The cellular system 207 may utilize "seed" user terminals. For example, a system operator may employ one or a mixture of fixed user terminals around the cell 220 to support the method described above with respect to FIG. 4 . 5 illustrates a cellular system 350 utilizing seed terminals 355 and 360 in accordance with an embodiment of the present invention. The seed terminals 355 and 360 may be in communication with the base station 365 in the cell 370 . The user terminal 375 may be in communication with the base station 365 . The base station 365 is in communication with the core network 380 . When the user terminal 385 is near the seed terminal 355 , 360 or the user terminal 375 and is powered on or waking up from a sleep mode, cellular system information is obtained from the user terminal 375 and the seed terminal 355 , 360 . Attempts to obtain and use the best cellular system information from devices according to the method described above with respect to FIG. 4 . In addition to obtaining information when a user terminal is powered on or waking up from a dormant mode, the seed terminal 355, 360 can be used to exchange other parameters, which may occur, for example, periodically or when entering a new cell. can

The use of seed terminals 355 and 360 is beneficial in several ways. First, the seed terminals 355 and 360 can be plugged into a power source, so battery life is not their concern. Second, since the seed terminals 355 and 360 are fixed, these parameters will be maintained in a timely manner for a long time. Third, the seed terminals 355 and 360 are always present within the cell 370 , whereas the mobile user terminals (eg, user terminals 375 ) can come and go. This increases the likelihood that the new user terminal 385 will be able to obtain useful system information without communicating with the base station. Fourth, the seed terminals 355 and 360 may be configured to perform only minimally necessary interactions with the cellular system 350 in order to keep the parameters current. In addition to supporting neighbor-assisted user terminal adaptation, seed terminals 355 , 360 may be used to perform relaying to cellular system 350 .

Proximity mobiles may be a fixed unit that provides a localized broadcast with information about neighboring cells, initial discovery parameters, network availability information, and the like. In particular, background scanning for the (home, higher priority) network is a rather battery-consuming operation. It is helpful to have information about the promising success of background scanning.

Alternatively, mobile seed terminals may be utilized. For example, mobile seed terminals may be deployed on city buses or trains within a cellular service area. These types of mobile seed terminals will provide user terminals on a bus or train with all the advantages described above with respect to a stationary user terminal.

A cellular system may utilize a centralized architecture. For example, if the cellular system is, for example, a 4G system and the user terminal has WLAN capability, the user terminal may report its measurements to the central node. The central node may include, for example, a desktop computer that compiles measurement reports and broadcasts them over the WLAN. In order to ensure that the information is not outdated, all participating user terminals need to periodically report their measurements. Such centralized control may enable filtering of information. For example, if a user terminal reports information that is very different from the rest of the participating user terminals, such information is probably erroneous (or of little value to most other terminals). This can be viewed as a generalization of the ping-pong aspect described below.

To implement the ping-pong aspect, a pair of user terminals may assist each other over time. Referring to FIG. 3 , the user terminal 205 may adapt the parameter based on information from the user terminal 200 for the first time. Subsequently, when the user terminal 205 is kept active and the user terminal 200 becomes inactive, when the user terminal 200 is activated again, it may not have an accurate parameter. For example, it cannot determine whether it was moving during its inactive state. Accordingly, as the user terminal 200 transitions to the active mode, current parameters are acquired again from the user terminal 205 .

An exchange of parameters is utilized to perform network or system selection. e.g. WLAN, different cellular systems (new phones capable of multimode operation: e.g. Integrated Digital Enhanced Network ("IDEN")/Global System for Mobile Communications ("GSM"), code Multiple systems may be available at a given location, such as division multiple access ("CDMA")/GSM) or different carriers. Instead of scanning multiple bands with other techniques, a user terminal can instead obtain this information from neighboring user terminals.

The exchange of parameters may be utilized to perform a random access channel ("RACH") "cooperative game" to avoid collisions. For example, UEs may avoid or agree to time-sharing a specific RACH resource, such as a RACH code or timeslot. Alternatively, parameters may be utilized to perform non-real-time ("NRT") traffic distribution, ie two user terminals coordinate with each other to ensure that they do not require large bandwidth at the same time. Moreover, when two user terminals request the same item (eg, the first broadcasting of a specific song on the Internet), it may receive this from the base station and relay it to the second user terminal. It can be fed into a virtual drive-in theater concept/4G unit as a WLAN access point.

In another embodiment where the cellular system utilizes TDD, the user terminal 205 may obtain a limited amount of information from the user terminal 200 without any direct interaction between the user terminal 205 and the user terminal 200 . . For example, the user terminal 205 may leave the receiver on both the downlink and uplink portions of the TDD frame, or it may leave the receiver continuously if it has no information about frame timing. When the user terminal 200 is transmitting to the base station 210 on the uplink, the user terminal 205 will receive the signal, which is high power since the user terminal 205 is in close proximity to the user terminal 200 . will be received as Then, the user terminal 205 may infer some information from the uplink transmission of the user terminal 200 . For example, the timing advance may be determined from the start time of the transmission of the user terminal 200 .

In another embodiment, semi-active monitoring is implemented. For example, only the user terminal 200 transmits the user ID through the WLAN system. Then, the user terminal 205 obtains appropriate parameters by monitoring the control message between the base station 210 and the user terminal 200 . Another way to learn the user ID without WLAN capability is for the user terminal 200 to include the user ID in the uplink transmission, so the user terminal 205 decodes the user ID by monitoring the uplink transmission of the user terminal 200 . can do.

According to a further embodiment, in-band monitoring is performed. The user terminal 200 synchronized to the base station 210 may transmit the location-dependent parameter in-band at a low transmit power level instead of using the WLAN channel. The location of the in-band transmission may be (a) an unused portion of the downlink frame, such as an unused sub-carrier, such as a DC sub-carrier, (b) a transmission on at least a portion of a RACH channel, or (c) a cellular system using TDD In the case of using , it may be transmission during turn-around time from downlink to uplink.

According to these ideas, information about the cellular system and/or user operating conditions, parameters, and lists of neighboring base stations for handing over calls is obtained directly from nearby user terminals in an accurate and timely manner. Despite the general reduction in the overall overhead burden on cellular system resources, these advantages arise.

A person skilled in the art can make a wide variety of modifications, changes and combinations to the above-described embodiments without departing from the spirit and scope of the present invention, and such modifications, changes and combinations are within the scope of the spirit according to the present invention. You are well aware that you can see what is inside.