Method and system for characterizing a radio channel of a wireless network using variability of synchronization

A speed parameter or channel quality parameter are determined in a mobile device based on variation in frequency offset measurement. A higher variation in the frequency offset measurement reflects a poorer channel quality and a higher speed; a lower variation in the frequency offset measurement reflects a better channel quality and a lower speed. The parameter(s) may be fed back to the system and used, for example, to make adaptive modulation and coding decisions.

FIELD

The application relates to methods and systems for characterizing a radio channel of a wireless network.

BACKGROUND

In a wireless environment, impairments of communication channels can affect significantly the performance of a wireless system. Multi-path fading is one of the most significant impairments.

Wireless communication systems such as CDMA, WCDMA, GSM/EDGE typically require accurate timing or synchronization with a base station and this is obtained from the estimation of the frequency of the received RF signal at a mobile device. In some wireless communication systems, the minimum level of accuracy of the frequency is 0.1 part per million (0.1 ppm). However in a typical design this will be about 0.04 ppm and this is achieved through the AFC (automatic frequency controller) system of the mobile device. The AFC system measures the frequency difference between the received RF signal and an onboard frequency and applies a correction in terms of a DC voltage offset to a correction feedback loop to keep the onboard frequency synchronized to the received signal. The onboard frequency may for example be based on a voltage controlled temperature compensated crystal oscillator (VCTCXO) that is relatively stable over a reasonable period of time, so that it can be used for the purpose of measuring Doppler effect to a certain level of accuracy. However, it is difficult or impossible to predict the exact Doppler shift (or frequency offset) at the mobile device for a given moment in time. This can be attributed to many factors such as multi-path (multiple routes a signal take from the base station to the mobile device), other fading effects due to environmental changes, the variability between base station line-of-sight and the direction of travel of the mobile device, etc.

DETAILED DESCRIPTION

According to a broad aspect, the application provides a method comprising: receiving a signal over a wireless communications channel; making a plurality of frequency offset measurements in respect of the signal; determining a measure of variation of the frequency offset measurements; determining at least one of a channel quality parameter and a speed parameter as a function of the measure of variation of the frequency offset measurements.

According to another broad aspect, the application provides a mobile device comprising: at least one antenna for receiving a signal; a local frequency source; a frequency offset determiner configured to determine frequency offset measurements between a frequency of the local frequency source and a frequency of the signal; a parameter determiner configured to determine a measure of variation of the frequency offset measurements and to determine at least one of a channel quality parameter and a speed parameter as a function of the measure of variation of the frequency offset measurements.

According to another broad aspect, the application provides a computer readable medium having instructions stored thereon for execution by a mobile device, that when executed, cause the mobile device to execute a method comprising, in respect of a signal received over a wireless communications channel: making a plurality of frequency offset measurements in respect of the signal; determining a measure of variation of the frequency offset measurements; determining at least one of a channel quality parameter and a speed parameter as a function of the measure of variation of the frequency offset measurements.

Applicant has observed that the frequency offset of the signal received at a mobile device at various instances in time is somewhat random in nature. Applicant has also observed that the degree of variation of the frequency offset of the received signal is proportional to the speed (or motion) of the mobile device and/or rate of change of the surrounding environment.

A simple example to explain this phenomenon will be described with reference toFIG. 1. Consider a scenario where a car60or pedestrian62is moving in an environment as shown inFIG. 1carrying a mobile device. The mobile device updates its timing (or synchronizes) by measuring the frequency offset of a signal received from a base station61at time intervals and let this be at t1, t2and t3. The position of the pedestrian62at time t1, t2, t3is indicated at70, and the position of the vehicle60at times t1, t2, t3is indicated at72. Suppose a mobile device moves through this environment at a constant speed of v with an on board clock set to hold the previous frequency accuracy. The mobile device in the vehicle picks up a signal (for example, the strongest component of a multi-path signal) at different points xv(t1), xv(t2), xv(t3) with delays (dt1, dt2and dt3), which are the time differences between the expected and the actual received signals. The mobile device performs time compensation based on these differences. The mobile device moving at pedestrian speed picks up the signal at positions xp(t1), xp(t2) and xp(t3). The path taken by signal to xp(t1) and xp(t2) is basically the same, and results in a delay of about dt1for both paths (only one shown). Subsequent to time compensation, the mobile device measures residual error as frequency offset Δf at each point. The following relationship exists between Δf and Δv:

Δ⁢⁢f=Δ⁢⁢vλ
where λ is the wavelength of the signal in free space and is a constant for most practical purposes (it may changes slightly under extreme changes in environmental conditions), and Δv=change in velocity over the same time period. The measured frequency offset can vary between the limit of the control loop of the synchronization circuit and the maximum allowed value of the system; for example these can be 40 and 500 Hz for a signal at 1 GHz. It has been observed that in the case of a pedestrian moving from xp(t1) to xp(t2), the variation in the frequency offset Δf, which is obtained from the received signal only from dt1will be small. In contrast, for a vehicle moving from xv(t1) to xv(t2), the frequency offset Δf, is measured at dt2from the signal at dt1, and the variation in the frequency offset is relatively large compared to the pedestrian case.

FIG. 2is a block diagram of a mobile device. The mobile device has an antenna10, RF (radio frequency) front end12, and frequency offset determiner14. Also shown is a parameter determiner16that determines one or more parameters based on the variation in frequency offset. In the specific example illustrated, parameter determiner16includes a channel quality parameter determiner18which produces a channel quality parameter output19and a speed parameter determiner20which produces a speed parameter output21.

In operation, a signal is received through the antenna10and the RF front end12. The frequency offset determiner determines the frequency offset. The frequency offset measurement is reflective directly or indirectly of a frequency difference between a frequency of the received signal and a frequency in the mobile device. The parameter determiner takes multiple instances of the frequency offset measurement and determines at least one parameter based on the variation of the multiple instances of the frequency offset measurement. For example, the variance of the frequency offset measurements may be used in determining the channel quality parameter and/or speed parameter. In the specific example shown, the channel quality parameter determiner18determines a channel quality parameter as a function of variation in the frequency offset measurement. The speed parameter determiner20determines a speed parameter as a function of variation in the frequency offset measurement.

FIG. 3is a block diagram of a mobile device that is a specific example of the mobile device ofFIG. 1. The mobile device again has an antenna10and RF (radio frequency) front end12. In this case, the functionality of frequency offset determiner14ofFIG. 1is implemented in an AFC (automatic frequency controller)30. The AFC30locks the radio receiver to the desired RF signal. There are many designs/methods by which this could be achieved; one simple design/method is shown inFIG. 3. The RF front-end12typically contains components such as an antenna switch, duplexers/diplexers, band pass filters and a low noise amplifier. The RF front-end12is connected to a demodulator32that in the illustrated example includes a mixer34and I/Q demodulator36. Other or different demodulation components may be present. The output of the demodulator32is passed to base-band processor38. The base-band processor38produces a VCTCXO (Voltage Controlled Temperature Compensated Crystal Oscillator) control signal40which is input to a VCTCXO42which generates the main reference signal for the radio that is input to a PLL (phased locked loop)44. The PLL44contains a frequency synthesizer46and phase frequency detector (PFD). An output of the frequency synthesizer52is input to a VCO (voltage controlled oscillator)52which generates a frequency that is near that of the RF signal. An output of the PFD48is passed through loop filter50to the VCO52. It shows a very specific example of an AFC that generates frequency offset which can be used in determining a measure of variation in frequency offset. More generally, any circuit/method for determining these frequency offsets can be employed.

In operation, a received RF signal enters the mixer34and mixes with LO (local oscillator) signal from the VCO52to produce a mixed signal. In many cases, the mixed signal is a base-band signal and this goes to into the demodulator36and then to the base-band processor38, but the specifics of this depend upon the specific receiver design implemented. The base-band processor38generates the VCTCXO control signal40. The VCTCXO control signal40is representative of the frequency offset detected by the base-band processor38between the onboard reference clock or frequency and the frequency of the received signal. The PLL44will lock the VCO52based on the control signal from VCTCXO42. This process is repeated periodically so long as the receiver is on. The period of adjustment for this complete loop may for example be determined by a requirement in a wireless standard. InFIG. 3, point54, namely the point where VCTCXO control signal40is output by the base band processor38, is the data collection point for frequency offset measurements. Specifically, the VCTCXO signal produced by the baseband processor38is representative of frequency offset determined by the base band processor38. This is then used in the parameter determiner16as described previously.

Referring now toFIG. 4, shown is a flowchart of a method of determining a channel quality parameter or a speed parameter. In some embodiments, only the channel quality parameter is determined. In other embodiments, only the speed parameter is determined. In further embodiments, both the channel quality parameter and the speed parameter are determined. The method begins at block4-1with a mobile device receiving a signal over a wireless channel. In block4-2, the mobile device collects frequency offset measurements. Note that the frequency offsets need not be absolute measurements of the actual difference in frequency; in some embodiments, they may be scaled representations of the actual difference in frequency. In some embodiments, the mobile device, on an ongoing basis, makes adjustments to a frequency of a local frequency source to synchronize with a remote frequency source. In such a case, the adjustments made can be used as the frequency offset measurements. In some embodiments, a control voltage is generated that reflects the frequency offset. In this case, the control voltage may be an example of a frequency offset measurement. In block4-3, the mobile device determines a measure of variation of the frequency offset measurements. In block4-4, the mobile device determines a channel quality parameter and/or speed parameter as a function of the measure of variation of the frequency offset measurements. Block4-5is an optional block included in some embodiments, and involves transmitting the channel quality parameter and/or the speed parameter back to the source of the signal such as a wireless access network component, e.g. a base station.

In some embodiments, the speed parameter can be fed back directly; having determined speed, in some embodiments, the channel quality parameter can be determined and fed back. In some embodiments, the channel quality parameter can be determined directly from the variation in the frequency offset.

Determining Parameter(s) Based on Variation in Frequency Offset

Having collected frequency offset measurements, embodiments of the application provide for the determination of various parameters that are a function of variation in the frequency offset. Two specific examples are a channel quality parameter and a speed parameter, each of which are detailed further below.

In some embodiments, the collected frequency offset measurements are used to estimate a probability distribution function (PDF) of the frequency offset. The PDF is then used to determine a measure of variation in the frequency offset. Various techniques for determining an amount of variation from a PDF can be employed to determine the measure of variation in the frequency offset. For example, some measure of width of the PDF may be employed. In a specific example, “width” is determined as follows: normalize the PDF to have a peak of one; determine two points on either side of the normalized peak having a predetermined value (for example 0.5), and determining the distance (along the frequency offset axis) between the two points. The distance if the width of the PDF. In another specific example, the variance of the PDF is employed as the measure of variation. Measurement data shows that the distribution falls very close to the Standard Cauchy Distribution (or a form of Gaussian distribution), which is written as follows:

The larger the number of samples, the more accurate the estimate of the distribution; however, a larger number of samples may also cover a time period during which the mobility of the user changes, and as such there is a tradeoff between accuracy of the distribution, and the timeliness of the result.

In some embodiments, a number of frequency offset samples is employed that may not necessarily give an accurate overall picture of a corresponding PDF, and rather than generate a PDF first and then determine the variation from the PDF, an approach is employed that determines the variation directly from the set of samples. For example, samples over 20 seconds might be used to determine the variation in frequency offset.

Having collected the frequency offsets over some time interval, a channel quality parameter and/or speed parameter is generated as a function of those measurements.

In some embodiments, one sample per second is collected over N seconds (N=20 is a specific example), and at the end of each N seconds, an updated channel quality parameter and/or speed parameter is computed. Other sampling frequencies or durations can alternatively be employed. In other embodiments, a moving window of N seconds worth of samples is processed on an ongoing basis to generate a channel quality parameter and/or speed parameter.

The following is a specific example of a specific equation that can be used to determine a measure of variation of the frequency offset from a set of frequency offset measurements:

Variation in frequency offset within a time interval having samples from n=1, . . . , N:
F_offset_var=Max{ABS[measured_offset(n)−measured_offset(n−1)]
In words, the maximum of the absolute value of the difference between two consecutive frequency offsets, over the time period, is used as the measure of variation. More generally, some approaches involve determining differences between consecutive frequency offset measurements, and then determining the measure of variation based on the differences.

Advantageously, the determination of the measure of variability of frequency offset can take place without interacting with the network; the functionality takes place within the device. The methods do not require the mobile device to be connected or be in a call. In some embodiments, this system uses the normal requirements of typical wireless standards, where the mobile device is required to carry out periodic measurement for maintaining synchronization with the base-stations and there are no additional steps required that would result in significant additional energy cost to the mobile device's battery.

Channel Quality Parameter

Having determined a measure of variability of frequency offset, using for example one of the methods described above, a channel quality parameter is determined based on that measure. In general, the lower the variability in the frequency offset, the higher the channel quality; the higher the variability in the frequency offset, the lower the channel quality. In some embodiments, F_offset_var as defined above is used as the channel quality parameter.

Determining the channel quality parameter provides a channel characterization that can be viewed as a mechanism to estimate the fading effect; however, more generally, the methods provide a new channel quality parameter that may or may not directly be representative of the fading effect at a given instant of time. The new channel quality parameter can be used in any context where channel quality metric are used. Specific examples include making AMC (adaptive modulation and coding) decisions, and making data rate determinations.

Determining Speed Parameter

Having determined a measure of variability of frequency offset, using for example one of the methods described above, a speed parameter is determined based on that measure. In general, the lower the variability in the frequency offset, the lower the speed; the higher the variability in the frequency offset, the higher the speed.

In general, the speed parameter can be used in any context where speed information is used. In some embodiments, the speed parameter as a channel quality parameter, the assumption being that a higher speed equates to a lower channel quality and a lower speed equates to a higher channel quality. The speed parameter can then be used in any application where channel quality is used. Specific examples include making AMC (adaptive modulation and coding) decisions, and making data rate determinations.

The speed parameter does not necessarily need to fed back to the network. For example, in some embodiments the speed parameter is used to control operation of the mobile device. Examples of this type of operation can be found in commonly assigned co-pending U.S. publication no. 2008/0099563 entitled “Automatic Operation of a Wireless Device Based on Physical Speed” which is hereby incorporated by reference in its entirety.

In some embodiments, the speed parameter is determined simply as K×(measure of variation of frequency offset measurements) where K is a constant determined empirically or experimentally.

The speed parameter is determined as a function of variation in the frequency offset measurements. Various specific examples of this will now be described. A speed parameter is a parameter that is somehow reflective of the speed of the mobile device. To name a few specific examples, this might be an absolute or differential speed value, a categorization of speed into one of a plurality of ranges, an indication of a change of categorization of speed according to a plurality of ranges.

In some embodiments, the speed is estimated as:

Speed=1.1×F⁢⁢offset⁢⁢vartime⁢⁢interval
where F_offset_var is as defined above. More generally, the relationship to speed will depend on the form of the measure of frequency offset variation. The factor 1.1 is explained as follows:

In some embodiments, a set of two or more speed ranges are defined, and the variation in timing offset (or frequency offset) is used to categorize the speed of the mobile device into one of the two or more ranges.

In a specific embodiment, two ranges are defined. For example, it has been observed that there is a band of separation between driving (or fast changing environment) speeds and pedestrian (slow varying environment) speeds. A first range of frequency offset variation (however defined) is defined to correspond with pedestrian speeds, for example the range of 0 to 10 km/h. A second range of frequency offset variation is defined to correspond with vehicular speeds, for example, the range above 35 km/h These ranges are for the purpose of example only; different and/or additional ranges may be used. Thresholds in the measure of frequency offset variation can be used to distinguish between the different speed ranges. Note that, as indicated previously, this approach does not distinguish actual speed of the device from environmental effects.

In some embodiments, the above-described PDF-based approach is used. The measure of variation in frequency offset, as determined from the estimated PDF, is converted to a speed parameter. When observing the measurement data of the AFC, for a stationary or pedestrian case (or a serene environment) frequency offset will have a very narrow spread of distribution. As the mobile device speed increases (or for the rapid environment change), this spread will widen. In some embodiments, having determined the measure of variability of frequency offset from the PDF, this is used to determine one of a plurality of speed ranges; in other embodiments, the measure is converted to an actual speed estimate. A sample probability density function (PDF) for the distributions associated with these two cases is shown in theFIG. 5.

For the two cases ofFIG. 5, the above referenced Cauchy distribution with, t=0, s=12.5 for stationary case and s=25 yield a good approximation for vehicular speeds. These data are obtained from measurement data. The difference can be easily observed on the Cumulative Distribution as shown inFIG. 6.

In some embodiments, the minimum width of the PDF for the stationary case (which is similar to the pedestrian case) is due to the inherent limit of the accuracy for the AFC loop and it could be attributed to the noise in the feedback loop, short-term temperature drift, DSP resolution limits, etc. This width may set the lower limit for the speed estimate.

The period of frequency offset measurement is typically set by the service providers and this may for example be every 0.5 seconds. With this set interval the frequency offset measurement between two successive measurements will diverge in direct proportionality to the speed of the mobile. However there exists a lower limit for the speed detection and it can be calculated as follows:

v=Δ⁢⁢ff⁢(3⁢⁢ⅇ⁢⁢8)⁢(3.6)⁢⁢km⁢/⁢h
For example, if the possible frequency accuracy of the system is 0.4 ppm, then at 900 MHz, the frequency error will be +/−36 Hz. The possible worst case frequency error of a stationary mobile is 72 Hz over one second period. Since the frequency measurement is updated every 0.5 seconds, the error will be 36 Hz and this will correspond to a speed of

This would be the worst case instantaneous case. However, if one were to average 20 data points, eliminate the temperature compensation and other requirements, the speed will reduce to 20 km/h or less. This will imply that speed threshold can be set for 20 km/h, which will be well above the pedestrian speed and at the same it will be within typical speed limits of 40 km/h.

Measurement Results

In this section sample measurement data is provided. The measurement data presented here is for the case of mobile devices in a GRPS/EDGE network although a similar approach can be taken for narrow band CDMA or WCDMA. In these cases of WCDMA and CDMA networks, the measurement data will be taken from more than one code channel (fingers), which corresponds to taking measurement from more than one base station.

A large amount of data was collected in several cities under various conditions. In the interest of conciseness, two cases are presented.FIG. 7below shows raw measurement data for the frequency offset seen at the mobile device when camped on a real GPRS/EDGE Network. The data was logged for two different cases. The first case is for a mobile device traveling within a vehicle on city streets at city speeds, then on a highway at highway speeds, and finally back in the city at very low speed (less than 15 km/h). The second case is for a mobile device carried by a pedestrian walking through different levels and throughout a building.

FIG. 7shows raw test data for the two cases. The vertical axis shows the frequency offset as a function of time on the horizontal axis. Specifically, the y-axis is the measured frequency offset between the received RF signal and the mobile expected frequency, and the x-axis is time in seconds. Generally indicated at800is the data for the first case, and generally indicated at802is the data for the second case. The data seen inFIG. 7shows that in both cases there seems to be a large variation in frequency offset measurement, which is due to an artifact in the design of the mobile device used for the tests. The Automatic Frequency Control (AFC) loop used for synchronization allows the correction to drift within a certain band of error. This is important so as to avoid unnecessary rapid correction changes that may occur in deep fading situations.FIG. 8shows the same data set when the delta between the successive measurements is considered, referred to as “delta raw data”. The delta raw data for the first case is generally indicated at810, and the delta raw data for the second case is generally indicated at812. This is equivalent to removing the DC offset in the AFC loop. Here one can easily observe the distinct difference between the two cases of pedestrian and the vehicle. The variation in the frequency error measurement for the pedestrian is very small.

In some embodiments, a maximum change in frequency offset over an observation period is determined and this is converted to a speed parameter as described previously. In some embodiments, the speed parameter thus determined is used as a new channel quality parameter.

Advantageously, with this approach, there is no requirement for storage of a large amount of data. This approach is applied to the data for the first and second cases defined above, and the result is plotted inFIG. 9. Specifically, a frequency offset variation is determined as a maximum change in frequency offset over a 20 second interval, and the result is converted to a speed estimate:
1.1×F_offset_var/20

InFIG. 9, curve820shows the speed estimate computed from data for the first case, while curve822shows the speed estimate computed from the data for the second case.

FIGS. 10 and 11are plots of further data taken under different conditions. Specifically,FIG. 10shows the delta raw data for a further pedestrian case generally indicated at850, and shows the delta raw data for a further vehicle case for a drive through street and HW401 in the Toronto area, generally indicated at852. In that drive, there were many stops done in addition to the traffic lights.FIG. 11shows speed estimates determined from the delta raw data using the method described previously. Specifically, curve860is a plot of speed estimate for the further pedestrian case, and curve862is a plot of speed estimated for the further vehicle case. One can easily pick up the stops from the plots. The straight dashed line in the figure indicated at864corresponds to the speed of 20 km/h and might, for example, be used as a threshold for selecting between pedestrian vs. vehicular speeds.

Another Mobile Device

Referring now toFIG. 12, shown is a block diagram of a mobile communication device700that may implement mobile device related methods described herein. It is to be understood that the mobile device700is shown with very specific details for example purposes only.

A processing device (a microprocessor728) is shown schematically as coupled between a keyboard714and a display726. The microprocessor728controls operation of the display726, as well as overall operation of the mobile device700, in response to actuation of keys on the keyboard714by a user.

The mobile device700has a housing that may be elongated vertically, or may take on other sizes and shapes (including clamshell housing structures). The keyboard714may include a mode selection key, or other hardware or software for switching between text entry and telephony entry.

In addition to the microprocessor728, other parts of the mobile device700are shown schematically. These include: a communications subsystem770; a short-range communications subsystem702; the keyboard714and the display726, along with other input/output devices including a set of LEDS704, a set of auxiliary I/O devices706, a serial port708, a speaker711and a microphone712; as well as memory devices including a flash memory716and a Random Access Memory (RAM)718; and various other device subsystems720. The mobile device700may have a battery721to power the active elements of the mobile device700. The mobile device700is in some embodiments a two-way radio frequency (RF) communication device having voice and data communication capabilities. In addition, the mobile device700in some embodiments has the capability to communicate with other computer systems via the Internet.

Operating system software executed by the microprocessor728is in some embodiments stored in a persistent store, such as the flash memory716, but may be stored in other types of memory devices, such as a read only memory (ROM) or similar storage element. In some embodiments, the RAT-specific routing information are stored in the flash memory716. In some embodiments, the RAT-specific flow control parameters are also stored in the flash memory716. In addition, system software, specific device applications, or parts thereof, may be temporarily loaded into a volatile store, such as the RAM718. Communication signals received by the mobile device700may also be stored to the RAM718.

The microprocessor728, in addition to its operating system functions, enables execution of software applications on the mobile device700. A predetermined set of software applications that control basic device operations, such as a voice communications module730A and a data communications module730B, may be installed on the mobile device700during manufacture. In addition, a personal information manager (PIM) application module730C may also be installed on the mobile device700during manufacture. The PIM application is in some embodiments capable of organizing and managing data items, such as e-mail, calendar events, voice mails, appointments, and task items. The PIM application is also in some embodiments capable of sending and receiving data items via a wireless network710. In some embodiments, the data items managed by the PIM application are seamlessly integrated, synchronized and updated via the wireless network710with the device user's corresponding data items stored or associated with a host computer system. As well, additional software modules, illustrated as other software module730N, may be installed during manufacture.

The routing information selection function described previously is an example of functionality that is included in a software module stored in memory. Information identifying the mobile device can be stored in the Flash Memory716or RAM718. The information identifying the mobile device is transmitted to the routing information configuration server, via the wireless network710using transmitter752and antenna756. Configuration information received from the routing information configuration server for configuring the RAT-specific routing information on the mobile device is received via the wireless network710over the air by antenna754and receiver750. It may alternatively be preloaded at factory time or configured manually by the user or IT administrator. The configuration information may be stored in the Flash Memory716or RAM718.

Communication functions, including data and voice communications, are performed through the communication subsystem770, and possibly through the short-range communications subsystem702. The communication subsystem770includes a receiver750, a transmitter752and one or more antennas, illustrated as a receive antenna754and a transmit antenna756. In addition, the communication subsystem770also includes a processing module, such as a digital signal processor (DSP)758, and local oscillators (LOs)760. The specific design and implementation of the communication subsystem770is dependent upon the communication network in which the mobile device700is intended to operate. For example, the communication subsystem770of the mobile device700may be designed to operate with the Mobitex™, DataTAC™ or General Packet Radio Service (GPRS) mobile data communication networks and also designed to operate with any of a variety of voice communication networks, such as Advanced Mobile Phone Service (AMPS), Time Division Multiple Access (TDMA), Code Division Multiple Access (CDMA), Personal Communications Service (PCS), Global System for Mobile Communications (GSM), etc. Other types of data and voice networks, both separate and integrated, may also be utilized with the mobile device700. The particular devices under consideration here are multi-mode mobile devices, and as such they include hardware and/or software for implementing at least two RATs. More specifically, in a particular example, there would be a respective communication subsystem770for each RAT implemented by the device.

Network access may vary depending upon the type of communication system. For example, in the Mobitex™ and DataTAC™ networks, mobile devices are registered on the network using a unique Personal Identification Number (PIN) associated with each device. In GPRS networks, however, network access is typically associated with a subscriber or user of a device. A GPRS device therefore typically has a subscriber identity module, commonly referred to as a Subscriber Identity Module (SIM) card, in order to operate on a GPRS network.

When network registration or activation procedures have been completed, the mobile device700may send and receive communication signals over the communication network710. Signals received from the communication network710by the receive antenna754are routed to the receiver750, which provides for signal amplification, frequency down conversion, filtering, channel selection, etc., and may also provide analog to digital conversion. Analog-to-digital conversion of the received signal allows the DSP758to perform more complex communication functions, such as demodulation and decoding. In a similar manner, signals to be transmitted to the network710are processed (e.g., modulated and encoded) by the DSP758and are then provided to the transmitter752for digital to analog conversion, frequency up conversion, filtering, amplification and transmission to the communication network710(or networks) via the transmit antenna756.

In addition to processing communication signals, the DSP758provides for control of the receiver750and the transmitter752. For example, gains applied to communication signals in the receiver750and the transmitter752may be adaptively controlled through automatic gain control algorithms implemented in the DSP758.

In a data communication mode, a received signal, such as a text message or web page download, is processed by the communication subsystem770and is input to the microprocessor728. The received signal is then further processed by the microprocessor728for an output to the display726, or alternatively to some other auxiliary I/O devices706. A device user may also compose data items, such as e-mail messages, using the keyboard714and/or some other auxiliary I/O device706, such as a touchpad, a rocker switch, a thumb-wheel, or some other type of input device. The composed data items may then be transmitted over the communication network710via the communication subsystem770.

In a voice communication mode, overall operation of the device is substantially similar to the data communication mode, except that received signals are output to a speaker711, and signals for transmission are generated by a microphone712. Alternative voice or audio I/O subsystems, such as a voice message recording subsystem, may also be implemented on the mobile device700. In addition, the display716may also be utilized in voice communication mode, for example, to display the identity of a calling party, the duration of a voice call, or other voice call related information.

The short-range communications subsystem702enables communication between the mobile device700and other proximate systems or devices, which need not necessarily be similar devices. For example, the short-range communications subsystem may include an infrared device and associated circuits and components, or a Bluetooth™ communication module to provide for communication with similarly-enabled systems and devices.

The AFC functionality described previously which determines the frequency offset might for example be implemented as part of DSP section758. The speed parameter and/or channel quality parameter determination might for example be done in the processor section728.

Numerous modifications and variations of the present application are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the application may be practiced otherwise than as specifically described herein.