Invented by Satish Venkob, David Philip Hole, Rene Faurie, Remo BORSELLA, Werner Karl Kreuzer, Steven Michael Hanov, Malikie Innovations Ltd
The Malikie Innovations Ltd invention works as followsWhen a device operates in a stationary mode, and before the device needs to communicate data, an example disclosed method includes determining if a timing advance stored is valid. If the stored advance is invalid, a valid advance is determined prior to the device’s need to communicate data.
Background for Timing advanced enhancements for mobile communications
Base stations (BS) are connected to the core networks and relay communication to and from mobile devices (MS). Cells are the zones of radio coverage that a BS can communicate over wirelessly. To perform a data transmission, an MS must connect to the network within a cell that is hosted by a BS it can reach. When conditions warrant, the connection can be moved to other cells that are served by the same BS or a different BS with a handover procedure.
A BS can provide uplink and/or downstream channels to multiple MSs using time division and frequency multiplexing. In a GPRS, for instance, the BS can periodically broadcast bursts on a defined Broadcast Control Channel (BCCH), which divides time into discrete segments known as frames, and contains time slots for data transmission between a BS and MS. Data transfer between a BS and an MS is carried out through the time slots on each defined frequency channels. Logical channels are defined by their type of data and can be further classified as physical channels. They carry data (voice or packet data), control data, and traffic in both uplink and downstream directions. The MS receives control signals from the BS, and maintains synchronization with them in order to receive data and transmit it over certain logical channels.
In order to allow an MS to access the network to initiate a data transmission or to respond to a page sent by the BS over a paging channels, it can compete for medium access, transmitting an Access Request message to the BS via a channel that is defined specifically for this purpose. This channel is referred to as a Random Access Channel (RACH) in GPRS. The BS will respond over an access grant channel if the MS’s access request is received successfully. It will then assign downlink and/or ulink channels to be used for data transfer between the BS & MS. The downlink and uplink channels are a virtual connection that is maintained between the BS, MS for the duration of data transfer within the cell where the MS has camped. This is called a temporary blockflow (TBF).
Although it is possible for the MS to maintain synchronization when receiving frames from the BS downlink, the propagation delay must be considered in order to synchronize frames transmitted uplink by the MS and the BS. The MS can transmit data with a timing offset that is based on the time taken for a signal from the MS to reach the BS. This timing advance (TA) is used. The TA at the MS is a negative offset between the beginning of a downlink frame received and the start of an uplink frame transmitted. The BS can calculate the appropriate TA based on the arrival times for signals transmitted by MSs with a predetermined TA. (e.g. a TA of 0 corresponding no timing advance, or any other predetermined TA) and then communicate this information to MS.
In GPRS/EDGE, the RACH (Real Access Channel) is a logical uplink channel of a bidirectional Common Control Channel (CCCH). The RACH access is based on contention, which means that each device decides autonomously when to transmit and that there may be collisions. Contention-based accessibility allows devices to request uplink resources on the basis of their requirements, rather than being scheduled periodically and not used. The MS can transmit data to the BS in what is called normal bursts, which are nearly as long as a slot. A MS that transmits normal bursts must use the correct TA value due to the propagation times from the MS to BS. The MS does not know the TA value during the initial transmission phase over RACH. The current GSM/EDGE protocol requires that the MS use access bursts rather than normal bursts when transmitting over the RACH. Access bursts are characterized by a guard interval which is long enough to compensate for any unknown propagation delays to reach the BS. They also carry less data than normal bursts. After the initial access procedure (also known as initial timing estimation), the network assigns a TA value that is appropriate to the MS. The network can also update the value of the TA using packet timing advance channels (PTCCH) based, e.g. The continuous timing update procedure is a variation in the timing of the access bursts that are sent over the PTCCH uplink. The MS should avoid both procedures as they are overhead signaling expenses.
The TA can also be continuously updated during a TBF by requiring the mobile station to transmit access bursts in the uplink at specific occasions and the network to estimate the timing variance of these bursts over the PTCCH or the PACCH. TA can also be updated continuously during a TBF, by requiring that the mobile station transmits access bursts on the uplink only at certain times and for the network to estimate timing variances of these bursts using the PTCCH/PACCH. The current procedures for initial timing estimation and continuous advance timing update are inefficient and not needed by MSs that are fixed to a specific location or who’s movement is expected within a defined area. Below are described modifications to the BS, MS and/or the network’s operating behavior that will reduce the extent of the TA updating procedure for these fixed MSs. The MS can be configured to run in a stationary or moving mode. In the moving mode, the current TA update procedures are followed and in the stationary mode they are modified. The description is based on a GPRS/EDGE service, but the modifications can be incorporated in other services of similar nature.
In the stationary mode, it is not necessary to perform the initial timing advancement procedure on each initial access to radio resource in a cell. This is the case in the moving mode. Initial access is used in this context. The first transmission that is associated with data transmission from the MS into the network of the cell when there are no other data transfers in progress. Initial access is, for example, the first transmission made on RACH as part of TBF setup in response to data received from higher protocol layers. Initial access can also happen during contention-based transfers of data without TBF. In the stationary mode, instead, the MS saves the TA received during an earlier data transfer in the cell, and uses this value for any subsequent data transfers on that cell. Additional triggers may be defined to perform the initial estimation of timing during initial accesses. These triggers could include resetting the device, power cycling it or receiving a trigger via an interface that allows the user to initiate the initial estimation of timing when necessary. If a certain number of access attempts (using a previously stored TA) to a cell fails, the normal initial TA estimate may be performed. Note that the modifications to the TA updating and estimation procedures described in this document are not intended as a change to existing procedures to maintain or acquire synchronization with a cell (e.g. by monitoring the appropriate synchronization channel).
Since TA is associated to a cell, it’s necessary to perform the initial estimation of TA (RACH, with access bursts etc.). After cell selection, the normal initial TA estimation procedure (RACH with access bursts, etc.) must be used before data transmission. Any transmission that does not use existing access bursts. The TA can only be estimated when the device is ready for data transmission. This is because the device may move between the time it selects the cell and the data transfer. For an MS in stationary mode, the delay and signaling that are normally associated with TA estimation can be avoided if TA is determined in advance. The TA can be estimated periodically (e.g. by using RACH and access bursts), to ensure that the MS does not lose synchronization with a cell due to changes in channel conditions, radio environment or other factors. The TA can be made available before the data is needed to be transmitted. This allows features that rely on the TA to transmit the data to be implemented into the system.
In the GMM-ready state, the network is aware of the cell where the mobile is camped and can therefore immediately send an assignment message to that cell which may assign a downlink link to the MS. FIG. FIG. The MS responds to the immediate message by transmitting access bursts via the RACH in order to obtain a TA and acknowledge the assignment. The MS may then request a channel for uplink transmission using the TA value acquired. FIG. FIG. The TA acquisition with access bursts step is skipped, as the MS requests a uplink channel with normal bursts and its stored TA. The network knows only which routing area/location the device is located in in the GMM standby mode. It must therefore page multiple cells. FIG. FIG. The MS responds by requesting an access burst over RACH to request a downlink and valid TA value. FIG. FIG.4 shows the MS operating in stationary mode, receiving an immediate assignment of the downlink channel along with the page. The MS responds by using normal bursts and the stored TA for the assignment of the uplink channel. In this situation, the paging protocol may be modified so that data is included in the paging channels, and the response, which may acknowledge the data or request uplink resources, will be sent using normal bursts based on the stored TA. In these cases, avoiding TA signaling may reduce the time required for the uplink TBF to be established and/or the completion of the TBF in downlink data transfers.
If the network knows that bi-directional data transfer is needed (e.g. by using an uplink-downlink TBF), it can assign both uplink-downlink channels with immediate assignment. 5 . There is no requirement to submit a request for resources and then assign them before the uplink data may be sent.
Since a stationary MS will not have to make as many cell selections and the power constraints are not as severe, it may be possible to configure the MS to update the cell even when in standby mode. The network would be able to know the cell where the MS is located so it can still use the downlink procedure even when the MS is in standby mode. The network can fall back to a standard paging procedure if for some reason the MS does not respond to the immediate assignment. Alternatively, a MS in stationary mode can be configured to only operate in a ready and no standby states so that cell updates are performed in accordance with the current GPRS/EDGE specifications.
A MS can be configured so that it decides whether to use the optimized procedures described in the above paragraph or to continue with the current procedures if the TA value changes from the last value known. The MS can be configured to switch from stationary to moving mode when it believes that its stored value of TA is not accurate (or cannot determine if the stored value is likely to be correct). A new TA is then required. The MS can determine if the TA has changed by comparing the data transfer time to the last time it was updated, or to the last time a successful data transfer took place to validate the TA. The received signal strength measurements of neighboring cells can be used to determine the location “fingerprint” so that, if the measurements have not changed within a certain tolerance, there is a high probability that the device’s correct TA has not been changed in the cell that serves it. The MS could perform the following algorithm as an example:
Another method for detecting movement could be to use an accelerometer by the MS to detect if it has moved enough to cause the stored TA to become invalid. An MS can use an accelerometer, for example, to determine if at least some movement has occurred. If motion is detected, the previous TA values are invalid. Alternately, accelerometer input can be used to trigger a further evaluation (such based on GPS or neighbor cell measurements). To determine if the TA is different. GPS or satellite navigation can be used as an alternative to determine the device’s location, both for determining the TA and initiating the data transfer.
The MS can perform a reversion to the moving mode to obtain a new TA prior to a data transmission. TA updates may also be performed at a later time. Since an MS can perform cell selection without moving, it is possible to store multiple valid entries simultaneously for different serving cells.
4. Low-Rate PTCCH
Currently, MSs using the packet transfer mode receive advance timing updates by using the PTTCH channel. On the uplink, the PTCCH frames are periodically designated (i.e. The MS transmits a burst of access on a PTCCH designated sub-channel. The network will then indicate whether or not the TA should be increased. The network could provide less frequent PTCCH occurrences for MSs in stationary mode. This is because the MSs in packet transfer mode are almost certain to not have moved between consecutive PTCCH occurrences, as specified in the existing standards. However, variations in time can still occur. An MS operating in stationary mode or packet idle mode could use a similar PTCCH subchannel (possibly occurring even less often) to validate and modify a stored value. This would be advantageous as it could increase the likelihood that a valid TA is available and allow the use of optimized scheme such as sending data over a RACH-like channels without setting up a TBF.
The use by an MS of the optimized procedures utilizing a stored TA as described above can be dependent on network permissions (e.g. as received in broadcast information or sent from point-to-point). The network may be able to determine if an MS is able to use the above procedures by the capabilities it signals to it. For example, if the MS indicates to the system that it can operate in the stationary mode. As an example, these MS’s could be classified as “zero-mobility” devices. Devices whose position remains fixed, or devices with a low mobility. Devices whose maximum range and/or speed of movement are below a specified threshold value. This scheme allows a device with zero mobility to operate more efficiently in stationary mode than a device with low mobility (which can operate in stationary modes from time to time). After the MS has communicated its classification to network, it could, for example, omit using the existing continuous timing advancement procedure for MSs that indicate zero mobility, but apply the same procedure or a low rate PTCCH optimized version of the procedure for devices with low mobile.Click here to view the patent on Google Patents.