Multimode mobile communication network search in a wireless communication device

A wireless communication device includes a wireless transceiver to wirelessly receive and transmit radio frequency (RF) signals and sample a signal representative of the received RF signal over a predetermined time period. The receiver stores the sampled signal in a memory. After the predetermined time period, a processor, coupled to the wireless transceiver and the memory, concurrently searches the sampled signal for multiple communication signals each operating according to a corresponding one of multiple, different mobile communication standards. If one of the communication signals is found, the WCD attempts to connect wirelessly with a communication network from which the found communication signal originates.

TECHNICAL FIELD

The present disclosure relates to network search techniques in wireless mobile communication devices.

BACKGROUND

Worldwide, wireless/mobile communication networks operate across a large number of frequency bands and according to many different mobile communication standards or RATs (Radio Access Technologies). A conventional wireless communication device (WCD), such as a smartphone, may be configured to operate with multiple ones of the different standards or RATs. Furthermore, there is no association between the WCD and the frequency band, as in general different WCDs can be used within different carriers of the same band. Different band arrangements for multiple RATs can be allocated by regulators in different countries or regions. Even within a given region, different operators may use a different RAT configuration in each available band, and even the same operator may change this setup over time.

Before communication services may be accessed by the WCD, the WCD must find or acquire an available network with which to connect. In a conventional WCD network search, the WCD selects a frequency band in which to search for a network that operates according to a given network standard, and tunes a receiver of the WCD to a potentially large set or number of candidate carriers of the selected band, where the set depends on the RATs being searched. While the receiver dwells on each of the selected frequency carriers for 5 or 10 milliseconds (ms), the WCD searches specific RF waveforms/signals received in that band for sequential frames of a downlink signal formatted according to each network standard. The WCD sequentially repeats the search process, i.e., dwell and downlink signal search, across all of the possible frequency carriers for each of the different networks (i.e., network standards) within a given band until the WCD finds an available network. The number of allocated bands worldwide is already in excess of 40, and is expected to grow further. The sequential search process is inefficient and time consuming given that there may be hundreds or thousands of search possibilities that are searched in sequence.

SUMMARY

A wireless communication device includes a wireless transceiver to wirelessly receive and transmit radio frequency (RF) signals, and sample a wide bandwidth signal representative of the received RF signal over a predetermined time period. The receiver stores the sampled signal (which may include I and Q samples) in a memory. After the predetermined time period, a processor, coupled to the wireless transceiver and the memory, concurrently searches the sampled signal for multiple communication signals each operating according to a corresponding one of multiple, different mobile communication standards or RATs. If one of the communication signals is found, the WCD attempts to connect wirelessly with a communication network from which the found communication signal originates.

DESCRIPTION OF EXAMPLE EMBODIMENTS

Embodiments are described herein in detail with reference to the accompanying drawings, wherein like reference numerals refer to like features throughout. The embodiments are intended as non-limiting examples. The figures described herein include schematic block diagrams illustrating various interoperating functional modules. Such diagrams are not intended to serve as electrical schematics and interconnections illustrated are intended to depict signal flow, various interoperations between functional components and/or processes and are not necessarily direct electrical connections between such components. Moreover, the functionality illustrated and described via separate components need not be distributed as shown, and the discrete blocks in the diagrams are not necessarily intended to depict discrete electrical components.

FIG. 1is a diagram of an example mobile communication network environment100in which a multimode network search technique described herein may be implemented. Network environment100includes a WCD104configured to transmit/receive appropriately formatted wireless communication signals106to/from multiple mobile communication networks110. Networks110operate according to different mobile communication air interface standards (also referred to as “modes” and “radio access types” (“RATs”)). Some of networks110may cover overlapping geographical areas while others have geographically separated coverage areas. Communication networks110may include, for example:a. a Long Term Evolution (LTE) network112that operates according to the LTE standard, such as 4G LTE;b. a Wideband Code Division Multiplex (WCDMA) network114that operates according to the WCDMA or International Mobile Telecommunications-2000 (IMT-2000) standard;c. a Time Division Synchronous Code Division Multiple Access (TD-SCDMA) network116that operates according to the TD-SCDMA standard; andd. a Global System for Mobile Communications (GSM) network118that operates according to the GSM standard.
Communication networks110may also include networks that operate according to mobile communication standards (i.e., RATs) different from those depicted inFIG. 1.

To access communication services, WCD104must first search for or acquire an available one of networks110and, if a network is found, establish connectivity with the found network. The terms “search for” and “acquire” and their derivatives (such as “searching for” and “acquiring,” etc.) are synonymous and used interchangeably herein. Each network, such as LTE network112, typically supports WCD communication in many different frequency bands as defined in the relevant standard, where a frequency band is identified by ranges of frequencies over which the WCD and the network can perform transmission and reception. For each RAT, a set of carrier frequencies is specified by the wireless communication standard(s). Each carrier frequency consists of a center frequency and a frequency bandwidth aligned with the center frequency. In some RATs multiple bandwidths may be specified for the same carrier center frequency. Thus, to access the communication services, WCD104typically searches for network availability among the many different possible networks (e.g., networks110) and, for each network, among different possible frequency bands and frequency carriers therein. The permutations and combinations of different networks and frequency bands translate to a large number of search hypotheses that may need to be searched by WCD104to find an available network.

Accordingly, WCD104implements an efficient, concurrent multimode (i.e., multi-RAT) network search technique to traverse the many possible search hypothesis quickly, and thereby reduce the time taken to find an available network. To do this, initially, WCD104records a signal received in an entire frequency band (or a large portion thereof) over a predetermined record time period, such as several milliseconds (ms). The predetermined record time period is sufficiently long to ensure that the recorded received signal would include several downlink signal frames from any available network, and wide enough in frequency to ensure that a large number of frequency carriers are contained within the recorded signal. As would be appreciated by one of ordinary skill in the relevant arts having read the present application, the aforementioned “signal” that is recorded may also be considered wide bandwidth energy (or a wide bandwidth energy spectrum) that is to be searched across the bandwidth for communication signals operating according to the different RATs. After the predetermined record time period, WCD104concurrently searches the recorded received signal (or a derivative representative metric thereof) for the presence of multiple communication signals each operating according to a corresponding one of multiple (different) RAT and possibly different frequencies. In other words, WCD104performs concurrent searches for the different networks that might be available based on the recorded received signal. In addition, WCD104may perform concurrent searches for a given network across different frequency bands/center frequencies, and over multiple candidate RATs. An advantage of this concurrent search technique is that a computer controller of WCD104may search for the different networks in parallel at a relatively fast controller processing speed (e.g., in the Gigahertz range) once the initial record time period of several milliseconds is over. The terms “concurrent” and “parallel” as used herein are synonymous.

With reference toFIG. 2, there is depicted an example block diagram of WCD104configured to perform the multimode search technique summarized above and described in detail below. Examples of WCD104include but are not limited to smartphones, laptop computers, tablet computers, and so on. WCD104includes a wireless transmitter (TX)206to transmit wireless RF signals via an antenna207, a wireless receiver (RX)208to receive a wideband wireless RF signal via the antenna, a sample buffer210to store digitized samples representative of the received RF signal, a controller212to control WCD104and perform the network search technique described herein, a controller memory214to store instructions and data used by the controller, and a user interface216to provide data to and receive data from a user or user applications (not shown inFIG. 2).

Controller212provides transmitter and receiver control signals213(e.g., dwell time control, center frequency tuning control, and frequency bandwidth control) to TX206and RX208to control the TX and RX so as to perform their respective operations described below.

RX208includes an RF front-end (FE)208ato tune to a communication frequency band at which an RF signal is to be received (e.g., a frequency band having a center frequency of 2.1 GHz and a frequency bandwidth of 50 MHz), frequency-downconvert the received RF signal around the center frequency to a baseband signal at a baseband frequency (or a near baseband frequency), and provide the baseband (or near baseband) signal to an analog-to-digital converter (ADC)208b. The aforementioned “RF signal” and “baseband signal” each refer to a relatively wideband signal that may encompass many RAT frequency bands. RX208may be configured to receive and process RF signals associated with mobile communication networks over a wide range of RF frequencies from, e.g., 200 Megahertz (MHz) to 2 or 3 GHz. TX206is configured to process and transmit RF frequencies over a frequency range similar to that of RX208. Other receive and transmit frequency ranges are possible. Also, both TX206and RX208are configured to tune their respective transmit and receive frequencies in increments sufficiently fine as to be aligned with communication signals associated with the various networks, e.g., in 1 Kilohertz (KHz) increments or less.

ADC208bdigitizes, i.e., samples, the (wideband) baseband signal delivered from RF FE208ato produce a sequence of samples representative of the received RF signal. ADC208bsamples the baseband signal at an effective sample rate sufficiently high, e.g., 250 MHz, to produce the samples with a frequency bandwidth sufficiently wide as to encompass the whole of or a significant portion of the frequency band of interest, such as a bandwidth in a range of 50-100 MHz. In an embodiment, ADC208bproduces quadrature samples, i.e., both I and Q samples that are 90° out-of-phase with respect to each other.

A LPF208clow-pass filters the samples from ADC208baccording to a low pass frequency bandwidth of the LPF, to produce filtered samples226representative of the received RF signal. The LPF frequency bandwidth may be set according to a bandwidth control signal from controller212via control signals213. Example frequency bandwidths may correspond to the frequency band of interest, such as 50, 25, 10, 5, 3, and 1.25 MHz. LPF208cprovides filtered samples226to sample buffer210and controller212. Filtered samples226are referred to herein as “sampled signal” that is representative of the received RF signal. In another embodiment, LPF208cmay be omitted so as to avoid frequency-limiting a bandwidth associated with the samples from ADC208b.

Sample buffer210includes sufficient storage space to store the samples226over a predetermined time period, such as 5 or 10 ms, although other time periods are possible. In other words, sample buffer210stores time segments of sampled signal representative of corresponding time segments of the received RF signal. The sampled signal may include both I and Q samples in the quadrature embodiment mentioned above. Sample buffer210may include any of a random access memory (RAM), magnetic disk storage media devices, optical storage media devices, flash memory devices, electrical, optical, or other memory storage devices.

Controller212is configured to perform the search techniques described herein based on the sampled signal stored in sample buffer210. Controller212may include a digital baseband processor, such as a digital signal processor, to perform processing of communication signals on behalf of both TX206and RX208, including, but not limited to, encoding/decoding, modulation/demodulation, and filtering. Controller210may also include a control processor to perform high-level control of WCD104and network search techniques. Controller212accesses the sampled signal in sample buffer210and computer instructions and data in memory214.

Memory214may comprise read only memory (ROM), random access memory (RAM), magnetic disk storage media devices, optical storage media devices, flash memory devices, electrical, optical, or other physical/tangible (e.g., non-transitory) memory storage devices. Thus, in general, the memory214may comprise one or more computer readable storage media (e.g., a memory device) encoded with software comprising computer executable instructions and when the software is executed (by the controller212) it is operable to perform the operations described herein. For example, memory214stores or is encoded with instructions for Multimode Network Search logic220to perform search techniques described herein. Multimode Network Search logic220may include (i) Frequency Scanning logic224to perform fast Fourier transforms (FFTs) and frequency-based received signal strength indication (RSSI) and analysis, and (ii) Network Cell Search logic226to perform concurrent mobile communication network cell searches for the different network RATs.

In addition, memory214stores data used and/or generated by logic220, such as a RAT parameter/constraint database230that includes multimode RAT parameters and search constraints associated with the different network RATs, such as the LTE, the WCDMA, the TD-SCDMA, and the GSM RATs. Parameter/constraint database230may include a separate RAT dataset for each of the different RATs. Each RAT dataset lists the various parameters associated with the given RAT, such as the frequency bands and sub-bands, various operating bandwidths, duplex modes, etc. An example LTE dataset is shown inFIG. 7.

With reference toFIG. 3, there is depicted a flowchart of an example method300of performing a multimode network search performed in WCD100under control of controller212. Controller212executes logic220to perform method300.

At305, controller212selects a frequency band of interest to be searched for active, available communication networks. Since RATs often define both frequency bands and sub-bands, the term “frequency band” as used herein refers generally to both “frequency band” and “frequency sub-band.” RX208tunes to the selected frequency band, for example, to a frequency band centered at 2.1 GHz and having a bandwidth in a range of 20-50 MHz. Also, the frequency bandwidth of LPF208cis configured as appropriate for the selected frequency band. RX208receives wireless RF signal in the selected frequency band. In an embodiment of RX208in which LPF208cis omitted, RX208captures signal over a much wider frequency bandwidth, e.g., up to 1 GHz.

At310, controller212causes sample buffer210to store samples226over a predetermined time period, such as 5 to 10 ms, although longer or shorter times as possible. The samples stored in sample buffer210, i.e., the sampled signal (or sampled energy spectrum), represent the received RF signal (or received RF energy spectrum). The time period is sufficiently long to capture several sequential frames of downlink signals of networks of interests. For example, the time period should be sufficiently long to capture 6 or 7 sequential Resource Blocks (RBs) in a downlink signal of the LTE RAT.

At next operations315-340, controller212accesses the sampled signal representative of the RF signal stored in sample buffer210and the network parameter/constraint datasets in database230and processes the sampled signal based on the datasets to concurrently search for different RATs, as described below.

At315, controller212converts the sampled signal from a time domain to a frequency domain using, e.g., an FFT, and performs an RSSI scan in the frequency domain. The RSSI scan detects energy levels at frequencies across the frequency domain.

At318, controller212assigns priorities to the frequencies based on their respective detected energy levels. Frequencies having relatively higher and lower detected energy levels are assigned relatively higher and lower priorities, respectively. Controller212selects the higher priority frequencies, and assigns the selected frequencies each to a corresponding one of concurrent network search threads or signal processing channels used in next operation320. In an embodiment, a single frequency having a highest detected energy level may be assigned to each of the search threads. In another embodiment, different frequencies may be assigned to different search threads. Also, at318, controller212assigns to each of the search threads a corresponding RAT to be searched in that search thread.

At320, controller212concurrently searches the sampled signal for multiple communication signals each operating according to a corresponding one of multiple, different RATs (assigned at318). To do this, controller212concurrently executes (parallel) search threads320a,320b,320c, and320deach to search for a communication signal that operates, at the assigned one of the selected frequencies, according to a corresponding one of the LTE, WCDMA, TD-SCDMA, and GSM RATs, for example. Search threads320a,320b,320c, and320deach search for the corresponding communication signal (e.g., network downlink signal) within a frequency bandwidth (of the sampled signal) that is centered-around the assigned frequency. In an embodiment in which RX208captures signal over a wide bandwidth such as 1 GHz, the assigned frequency may be set equal to any frequency in the wide-bandwidth, e.g., at 1 MHz, 10 MHz, 500 MHz, 750 MHz, and so on. A given one of search threads320a-320dmay itself represent multiple concurrent search threads to concurrently search for an assigned network at multiple different frequencies. Search threads320a,320b,320c, and320dmay be implemented as concurrent, separate signal processing channels, as describe below in connection withFIG. 4.

At325, controller212determines whether a network was found at320. If a network was not found, flow proceeds to305and the process repeats with a new selected frequency band. If a network was found, flow proceeds to330.

At330, controller212determines whether the found network is suitable by checking the broadcast information channel to ensure that the WCD is allowed to establish a connection with the network according to the relevant cell suitability criteria defined in each specific standard for a specific RAT. If the found network is suitable, flow proceeds to335.

At335, controller212causes WCD104to connect and register with the found network, after which the WCD may wirelessly access mobile communication services through the found network. To connect and register with the found network, TX306transmits appropriately formatted uplink signals to and RX308receives downlink signals from the found network.

If it was determined that the found network was not suitable at330, flow proceeds to340. At340, controller212updates network constraints/parameter database230to indicate the unsuitability of the found network or unsuitability of certain features of the found network. For example, the RAT dataset in database230corresponding to the RAT determined to be unsuitable at330may be updated to reflect that the frequency carrier selected at305in the RAT is not available (as determined at330), but the other frequency bands are still available for search. From340, flow proceeds to318for a search reprioritization based on the updated database230.

The above described process repeats over time.

With reference toFIG. 4, there is depicted a sequence of operations400expanding on and representative of any one of search threads320a,320b,320c, and320d. Collectively, operations400also represent a digital signal processing channel (corresponding to any of search threads320a-320d) that processes the sampled signal in sequential stages to search for a given RAT. As mentioned above, at operation318, a selected frequency and a selected RAT to be searched are assigned to search thread operation400.

At405, controller212frequency-shifts, e.g., frequency mixes, a frequency spectrum of the sampled signal to a baseband frequency (e.g., zero Hz) if the assigned center frequency is offset from the baseband frequency. This enables each search thread to tune-to/cover a different portion of the selected frequency band to which RX208tuned-to in operation305and represented in the frequency spectrum/domain produced by the FFT in operation315. For example, a first search thread may frequency-shift the frequency spectrum by a first assigned frequency, a second search thread may frequency-shift the frequency spectrum by a second assigned frequency, and so on across the multiple search threads. An example of this will be discussed below in connection withFIGS. 5 and 6.

At410, controller212decimates the sampled signal, i.e., (i) low pass filters the sampled signal with a low pass frequency bandwidth suitable for purposes of anti-aliasing and capturing a bandwidth of a downlink signal of interest, and (ii) down-samples the low pass filtered, sampled signal. Operation410produces decimated samples.

Operations405and410collectively represent a channel signal conditioning operation in which controller212conditions the sampled signal prior to operation415, described below.

At415, controller212performs a network cell search on the decimated samples according to the assigned RAT. The cell search is a basic function in a mobile communication system in which time and frequency synchronization between the WCD and the mobile communication network is achieved. Typically, the WCD acquires time and frequency synchronization by processing a downlink synchronization channel from the mobile communication network. For example, for LTE, a network cell search includes the following high-level operations based on processing of network downlink frames recorded in the received signal: detecting symbol timing and a frequency offset; detecting a cell identifier (ID) group, frame timing, and other cell specific information; and detecting a cell ID from downlink reference signals. Generally, any heretofore known or hereafter developed network cell search technique may be used for the cell search, as would be appreciated by one of ordinary skill in the relevant arts after having read the present description.

FIGS. 5 and 6collectively represent an example of a search strategy implemented in method300.FIG. 5is a graph of an example FFT frequency spectrum500(i.e., frequency domain plot) of the sampled signal produced by an FFT operation at315. Note that the frequencies represented in frequency spectrum500are frequency down-converted from corresponding RF frequencies by RX208.FIG. 6is an excerpt of the flowchart inFIG. 3that shows prioritization operation318and various concurrent search threads320a-320dand602-608each annotated with assigned search parameters, including a respective center frequency (CF) fromFIG. 5, and a frequency bandwidth (BW) associated with the assigned CF.

With reference toFIG. 5, prioritization operation318assigns descending priorities P1, P2, and P3to center frequencies F1, F2, and F3of spectrum500in accordance with detected energies of the frequencies. Then, operation318assigns various ones of CFs F1, F2, and F3and corresponding BWs to corresponding ones of the concurrent search threads depicted inFIG. 6based on priorities P1, P2, and P3and bandwidth information from network datasets in database230. With reference toFIG. 6, search parameters CF and BW are assigned to each of the concurrent search threads, as follows:a. WCDMA search320b: CF F1and BW=5 MHz;b. TD-SCDMA search320c: CF F1and BW=5 MHz;c. GSM search320d: CF F2and BW=10 MHz; andd. LTE search320ais divided into multiple concurrent search threads602-608each assigned to perform a respective LTE cell search based on the following parameters that account for a 125 KHz raster on the center frequency and different bandwidths defined in the LTE standard.i. LTE search602: CF F1and BW=3 MHz;ii. LTE search604: CF=F1+125 KHz and BW=3 MHz;iii. LTE search606: CF=F1+250 KHz and BW=3 MHz; andiv. LTE search608: CF=F1+375 KHz and BW=5 MHz.

Each of the above listed search threads may be implemented as a separate signal processing channel similar to channel400described above in connection withFIG. 4.

Many other search variations are possible beyond those depicted inFIG. 6. As can be seen in the example ofFIGS. 5 and 6, different RATs, center frequencies, and bandwidths may be searched concurrently by controller212based on a single recorded segment of the received signal.

With reference toFIG. 7, there is depicted an example LTE dataset700stored in database230. A similar dataset may be stored for each of the different RATs, as described above.

A method embodiment comprises: sampling a signal (or sampling an energy spectrum) received wirelessly over a predetermined time period; after the predetermined period, concurrently searching the sampled signal (or energy spectrum) for multiple communication signals each operating according to a corresponding one of multiple, different mobile communication standards; and if one of the communication signals is found, attempting to connect wirelessly with a communication network from which the found communication signal originates.

An apparatus embodiment comprises: a wireless transceiver to wirelessly receive and transmit radio frequency (RF) signals and sample a signal representative of the received RF signal over a predetermined time period; a memory to store the sampled signal; and a processor, coupled to the wireless transceiver and the memory, configured to: after the predetermined period, concurrently search the sampled signal for multiple communication signals each operating according to a corresponding one of multiple, different mobile communication standards; and if one of the communication signals is found, attempt to connect wirelessly with a communication network from which the found communication signal originates.

The descriptions above are intended to illustrate possible implementations of the present inventive concept and are not restrictive. Many variations, modifications and alternatives will become apparent to the skilled artisan upon review of this disclosure. For example, components equivalent to those shown and described may be substituted therefore, elements and methods individually described may be combined, and elements described as discrete may be distributed across many components. The scope of the invention should therefore be determined not with reference to the description above, but with reference to the appended claims, along with their full range of equivalents.