Synchronous spectrum sharing by dedicated networks using OFDM/OFDMA signaling

Abstract

A system and method for synchronous spectrum sharing for a dedicated network in a wireless communication system based on orthogonal frequency-division multiplexing (OFDM) or orthogonal frequency division multiple access (OFDMA) signaling is disclosed. The system and method includes detecting a frame of a broadcast waveform and extracting idle spectrum information from a subframe associated with the dedicated subchannel to the secondary user node. The system allows transmitting data from the secondary user node in unused symbol slots identified in the idle spectrum information thereby making efficient use of unused or idle spectrum. Accordingly, secondary users of the wireless communication system can dynamically form ad-hoc mesh network communications in fixed or mobile scenarios.

Description

TECHNICAL FIELD OF THE INVENTION

The present disclosure relates generally to communication networks and, in particular, to systems for synchronous spectrum sharing.

BACKGROUND OF THE INVENTION

Conventional fixed spectrum allocation schemes lead to significant spectrum under-utilization. For instance, experiments have indicated that as much as 62% of the spectrum below the 3 GHz band is idle even in the most crowed areas (e.g., near downtown Washington D.C. where both government and commercial spectrum usage is intensive). Such under-utilization and increasing demand for the radio spectrum suggest that a more effective spectrum allocation and utilization policy is necessary.

Currently, secondary users may use the licensed spectrum only when such use does not interfere with a primary user's communication. Such requirements imply that the use of the spectrum varies with time (i.e., dynamically changes), and is dependent on the load imposed by the primary users. Several conventional systems use multiple channels in wireless networks. However, such systems fail in dynamic spectrum access networks. For example, conventional systems assume that the set of available channels is static (i.e., the channels available for use are fixed at the time of network initiation). In multiple access wireless networks, however, such as Worldwide Interoperability for Microwave Access (WiMAX) with orthogonal frequency division multiple access (OFDMA) signaling, the set of available channels dynamically changes. Furthermore, conventional systems often assume that the available channels are “homogeneous” (i.e., different channels have similar range and support similar data rates). These assumptions do not hold true in situations such as, for example, where different channels are located on widely separated slices of frequency spectrum with different modulation schemes and different propagation characteristics. Moreover, conventional system fail to provide dedicated subchannels for private network users.

Therefore, there is a need for synchronous spectrum sharing systems based on orthogonal frequency-division multiplexing (OFDM) or OFDMA signaling. In particular, there is a need for synchronous spectrum sharing systems for dedicated networks using OFDM or OFDMA signaling.

SUMMARY OF THE INVENTION

The present disclosure provides a technique for synchronous spectrum sharing for dedicated networks based on orthogonal frequency-division multiplexing (OFDM) or orthogonal frequency division multiple access (OFDMA) signaling.

In one embodiment, the present disclosure provides a synchronous spectrum sharing system for use in a wireless communication system having a dedicated network subchannel associated with a broadcast frame. The system includes a frame detector configured to extract idle spectrum information for the dedicated network subchannel from a subframe within the broadcast frame. A secondary node transmits data in a first unused symbol slot identified in the idle spectrum information.

In another embodiment, the present disclosure provides a a method of synchronous spectrum sharing for use in a wireless communication network. The method includes detecting a subframe associated with a dedicated network subchannel from a broadcast waveform. The method also includes extracting idle spectrum information for the dedicated network subchannel from the subframe. The method further includes transmitting data in a first unused symbol slot identified in the idle spectrum information.

In another embodiment, the present disclosure provides a method of synchronous spectrum sharing for use in a wireless communication network having a primary user node and a secondary user node. The method includes detecting a frame of a broadcast waveform. The method also includes extracting idle spectrum information associated with a dedicated network subchannel of the frame to the secondary user node. The method further includes receiving data from the secondary user node in a first unused symbol slot identified in the idle spectrum information.

In still another embodiment, the present disclosure provides an apparatus for synchronous spectrum sharing ror use in an OFDM/OFDMA wireless communication system. The apparatus includes a secondary node configured to extract idle spectrum information from a subframe associated with a dedicated network subchannel of a broadcast frame. The secondary node transmits data in a first unused symbol slot identified in the idle spectrum information.

Before undertaking the DETAILED DESCRIPTION OF THE INVENTION below, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document: the terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation; the term “or,” is inclusive, meaning and/or; the phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like; and the term “controller” means any device, system or part thereof that controls at least one operation, such a device may be implemented in hardware, firmware or software, or some combination of at least two of the same. It should be noted that the functionality associated with any particular controller may be centralized or distributed, whether locally or remotely. Definitions for certain words and phrases are provided throughout this patent document, those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior, as well as future uses of such defined words and phrases.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure and its advantages, reference is now made to the following description taken in conjunction with the accompanying drawings, in which like reference numerals represent like parts:

FIG. 1 is an exemplary wireless network suitable for synchronous spectrum sharing according to one embodiment of the present disclosure;

FIG. 2 is an exemplary block diagram of an orthogonal frequency-division multiplexing (OFDM) transmitter according to one embodiment of the present disclosure;

FIG. 3 is an exemplary block diagram of an OFDM receiver according to one embodiment of the present disclosure

FIG. 4 depicts the insertion of a cyclic prefix (CP) to a data payload according to one embodiment of the present disclosure;

FIGS. 5A and 5B depict exemplary distributed sub-carrier allocations according to one embodiment of the present disclosure;

FIG. 6 is an exemplary OFDMA frame structure for a time division duplex (TDD) implementation according to one embodiment of the present disclosure;

FIGS. 7A and 7B are exemplary OFDMA frame structures having a dedicated network channel and an associated private user map (PU MAP) according to one embodiment of the present disclosure;

FIG. 7C is an exemplary OFDMA frame structure with secondary node packet bursts in unused OFDM symbol slots in the dedicated network channel according to one embodiment of the present disclosure;

FIG. 7D illustrates an exemplary cluster of secondary nodes found in a wireless network according to one embodiment of the present disclosure;

FIG. 8 is an exemplary secondary node data burst relative to an OFDMA frame structure for a given OFDM symbol period; and

FIG. 9 is a somewhat simplified a flow diagram illustrating a method of synchronous spectrum sharing according to one embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 through 9, discussed below, and the various embodiments used to describe the principles of the present disclosure in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the disclosure. Those skilled in the art will understand that the principles of the present disclosure may be implemented in any suitably arranged wireless communication system.

FIG. 1 illustrates an exemplary wireless network 100 suitable for synchronous spectrum sharing according to one embodiment of the present disclosure. In the illustrated embodiment, wireless network 100 includes base station (BS) 101, base station (BS) 102, and base station (BS) 103. Base station 101 communicates with base station 102 and base station 103. Base station 101 also communicates with Internet protocol (IP) network 130, such as the Internet, a proprietary IP network, or other data network.

Base station 102 provides wireless broadband access to network 130, via base station 101, to a first plurality of subscriber stations within coverage area 120 of base station 102. The first plurality of subscriber stations includes subscriber station (SS) 111, subscriber station (SS) 112, subscriber station (SS) 113, subscriber station (SS) 114, subscriber station (SS) 115 and subscriber station (SS) 116. In an exemplary embodiment, SS 111 may be located in a small business (SB), SS 112 may be located in an enterprise (E), SS 113 may be located in a WiFi hotspot (HS), SS 114 may be located in a first residence, SS 115 may be located in a second residence, and SS 116 may be a mobile (M) device.

Base station 103 provides wireless broadband access to network 130, via base station 101, to a second plurality of subscriber stations within coverage area 125 of base station 103. The second plurality of subscriber stations includes subscriber station 115 and subscriber station 116. In alternate embodiments, base stations 102 and 103 may be connected directly to the Internet by means of a wired broadband connection, such as an optical fiber, DSL, cable or T1/E1 line, rather than indirectly through base station 101.

In other embodiments, base station 101 may be in communication with either fewer or more base stations. Furthermore, while only six subscriber stations are shown in FIG. 1, it is understood that wireless network 100 may provide wireless broadband access to more than six subscriber stations. It is noted that subscriber station 115 and subscriber station 116 are on the edge of both coverage area 120 and coverage area 125. Subscriber station 115 and subscriber station 116 each communicate with both base station 102 and base station 103 and may be said to be operating in handoff mode, as known to those of skill in the art.

In an exemplary embodiment, base stations 101-103 may communicate with each other and with subscriber stations 111-116 using an IEEE-802.16 wireless metropolitan area network standard, such as, for example, an IEEE-802.16e standard. In another embodiment, however, a different wireless protocol may be employed, such as, for example, a HIPERMAN wireless metropolitan area network standard. Base station 101 may communicate through direct line-of-sight or non-line-of-sight with base station 102 and base station 103, depending on the technology used for the wireless backhaul. Base station 102 and base station 103 may each communicate through non-line-of-sight with subscriber stations 111-116 using OFDM and/or OFDMA techniques.

Base station 102 may provide a T1 level service to subscriber station 112 associated with the enterprise and a fractional T1 level service to subscriber station 111 associated with the small business. Base station 102 may provide wireless backhaul for subscriber station 113 associated with the WiFi hotspot, which may be located in an airport, cafe, hotel, or college campus. Base station 102 may provide digital subscriber line (DSL) level service to subscriber stations 114, 115 and 116.

Subscriber stations 111-116 may use the broadband access to network 130 to access voice, data, video, video teleconferencing, and/or other broadband services. In an exemplary embodiment, one or more of subscriber stations 111-116 may be associated with an access point (AP) of a WiFi WLAN. Subscriber station 116 may be any of a number of mobile devices, including a wireless-enabled laptop computer, personal data assistant, notebook, handheld device, or other wireless-enabled device. Subscriber stations 114 and 115 may be, for example, a wireless-enabled personal computer, a laptop computer, a gateway, or another device.

Dotted lines show the approximate extents of coverage areas 120 and 125, which are shown as approximately circular for the purposes of illustration and explanation only. It should be clearly understood that the coverage areas associated with base stations, for example, coverage areas 120 and 125, may have other shapes, including irregular shapes, depending upon the configuration of the base stations and variations in the radio environment associated with natural and man-made obstructions.

Also, the coverage areas associated with base stations are not constant over time and may be dynamic (expanding or contracting or changing shape) based on changing transmission power levels of the base station and/or the subscriber stations, weather conditions, and other factors. In an embodiment, the radius of the coverage areas of the base stations, for example, coverage areas 120 and 125 of base stations 102 and 103, may extend in the range from less than 2 kilometers to about fifty kilometers from the base stations.

As is well known in the art, a base station, such as base station 101, 102, or 103, may employ directional antennas to support a plurality of sectors within the coverage area. In FIG. 1, base stations 102 and 103 are depicted approximately in the center of coverage areas 120 and 125, respectively. In other embodiments, the use of directional antennas may locate the base station near the edge of the coverage area, for example, at the point of a cone-shaped or pear-shaped coverage area.

The connection to network 130 from base station 101 may comprise a broadband connection, for example, a fiber optic line, to servers located in a central office or another operating company point-of-presence. The servers may provide communication to an Internet gateway for internet protocol-based communications and to a public switched telephone network gateway for voice-based communications. In the case of voice-based communications in the form of voice-over-IP (VoIP), the traffic may be forwarded directly to the Internet gateway instead of the PSTN gateway. The servers, Internet gateway, and public switched telephone network gateway are not shown in FIG. 1. In another embodiment, the connection to network 130 may be provided by different network nodes and equipment.

FIG. 2 is exemplary block diagram of a typical OFDM/OFDMA transmitter 200 according to one embodiment of the present disclosure. Transmitter 200 constructs, for example, an OFDM/OFDMA composite signal by first passing the serial output of a formatted, encoded, interleaved data signal through serial-to-parallel converter 202. Serial-to-parallel converter 202 separates each data signal into parallel data streams (e.g., X₀ . . . X_N-1). A mapping function (MAP) within serial-to-parallel converter 202 maps each parallel data stream into I and Q modulation symbols, which are then applied to inverse fast Fourier transform (IFFT) block 204. The subcarrier separation is preferably an inverse of the symbol rate. IFFT block 204 computes the IFFT of each data stream and passes the output to parallel-to-serial and cyclic prefix (CP) block 206.

Parallel-to-serial and CP block 206 combines each parallel data stream into a data signal and introduces CP to aid in eliminating inter-symbol interference (ISI) and inter-block interference as later described in detail herein. Parallel-to-serial and CP block 206 sums the multiple subcarriers to the transmission frequency. For operation in time division duplex (TDD) mode, Parallel-to-serial and CP block 206 inserts a guard interval (GI) into the signal. The output of parallel-to-serial and CP block 206 is passed to windowing matched filter 208 and then to up-converter block 210. The output of up-converter block 210 is then passed to RF section block 212 and transmitted via antenna 214. Accordingly, in the example shown in FIG. 2, user data signals may be represented by a set of 2N subcarriers. In addition, pilot plus control signaling may be represented by a set of 2M separate subcarriers.

FIG. 3 is an exemplary block diagram of a typical OFDM/OFDMA receiver 300 according to one embodiment of the present disclosure. Receiver 300 detects the transmitted symbols and essentially reverses the process implemented by transmitter 200 described above. For example, the signal transmitted by antenna 214 is received by antenna 302. The signal is passed to transceiver and CP remove block 304. Transceiver and CP remove block 304 removes the CP from the signal and passes the signal to serial-to-parallel block 306. Serial-to-parallel block 306 separates the data signal into parallel data streams (e.g., X₀ . . . X_N-1). A MAP within serial-to-parallel converter 201 maps each parallel data stream into I and Q modulation symbols, which are then passed to fast Fourier transform (FFT) block 308. The output of FFT block 308 is then passed to parallel-to-serial and decoder block 310 and then output as desired.

FIG. 4 is an exemplary block diagram of system 400 having an OFDM/OFDMA frame detector 402 and a transceiver module 404 in accordance with one embodiment of the present disclosure. OFDM/OFDMA frame detector 402 detects signals received from transceiver module 404. The signal is passed to CP remove block 406. CP remove block 406 removes the CP from the signal and passes the signal to serial-to-parallel block 408. Serial-to-parallel block 408 separates the data signal into parallel data streams (e.g., X₀ . . . X_N-1). A MAP within serial-to-parallel converter 408 maps each parallel data stream into I and Q modulation symbols, which are then applied to FFT block 410. The output of FFT block 410 is passed to parallel-to-serial and decoder block 412 and then output to OFDM/OFDMA modem and detection engine 414.

FIG. 4 illustrates OFDM symbol 400 in which CP 402 is inserted into data payload 404 according to one embodiment of the present disclosure where the total symbol period (T_s) is greater than the sum of the guard times (T_g) and the useful symbol period (T_u). OFDM waveforms provide increased symbol duration (i.e., T_s and T_u) and thus improves the robustness of OFDM to delay spread. Accordingly, with the introduction of CP 402, ISI could be eliminated as long as the duration of CP 402 is longer than the channel delay spread. CP 402 is typically a repetition of the last samples of data portion of the block that is appended to the beginning of data payload 404 as shown in FIG. 4. CP 402 prevents inter-block interference and makes the channel appear circular. CP 402 therefore permits low-complexity frequency domain equalization. While CP 402 somewhat reduces bandwidth efficiency, the impact of CP 402 is similar to the “roll-off factor” in raised-cosine filtered single-carrier systems. Notably, OFDM has a very sharp, almost “brick-wall” spectrum. Thus, a large fraction of the allocated channel bandwidth may be utilized for data transmission and for moderating the loss in efficiency due to CP 402.

Similar attributes exist for OFDMA. The OFDMA symbol structure consists of three types of subcarriers: (1) Data subcarriers for data transmission; (2) Pilot subcarriers for estimation and synchronization purposes; and (3) Null subcarriers for no transmission (typically used for guard bands and DC carriers). Active subcarriers (i.e., data and pilot subcarriers) are grouped into subsets of subcarriers called subchannels.

In certain standards such as, for example, IEEE-802.16-2004 and IEEE-802.16-2005, the minimum frequency-time resource unit of subchannelization is one slot. One slot is typically equal to 48 data tones or subcarriers. The two types of sub-carrier permutations for subchannelization are the diversity permutation and the contiguous permutation.

The diversity permutation draws subcarriers pseudo-randomly to form a subchannel. Diversity permutation generally provides frequency diversity and inter-cell interference averaging as later shown in FIGS. 5A and 5B where there are 512 subcarriers. The diversity permutations include DL FUSC, DL PUSC, UL PUSC and other optional permutations. With DL PUSC, for each pair of OFDM symbols, the available or usable subcarriers are grouped into clusters containing 14 contiguous subcarriers per symbol, with pilot and data allocations in each cluster in the even and odd symbols.

A re-arranging scheme is used to form groups of clusters such that each group is made up of clusters that are distributed throughout the sub-carrier space. A subchannel in a group contains two (2) clusters and is comprised of 48 data subcarriers and eight (8) pilot subcarriers. Analogous to the cluster structure for DL, a tile structure is defined for the UL PUSC. The available sub-carrier space is split into tiles and six (6) tiles, chosen from across the entire spectrum by means of a re-arranging/permutation scheme, are grouped together to form a slot. The slot is comprised of 48 data subcarriers and 24 pilot subcarriers in three (3) OFDM symbols.

The contiguous permutation, on the other hand, groups a block of contiguous subcarriers to form a subchannel. The contiguous permutations include DL advanced modulation and coding (AMC) and UL AMC, and have the same structure. A bin consists of nine (9) contiguous subcarriers in a symbol, with eight (8) assigned for data and one assigned for a pilot. A slot in AMC is defined as a collection of bins of the type (N×M=6), where N is the number of contiguous bins and M is the number of contiguous symbols. Thus the allowed combinations are [(6 bins, 1 symbol), (3 bins, 2 symbols), (2 bins, 3 symbols), (1 bin, 6 symbols)]. AMC permutation enables multi-user diversity by choosing the subchannel with the best frequency response.

The IEEE-802.16-2005 Wireless MAN OFDMA mode is based on the concept of scalable OFDMA (S-OFDMA). S-OFDMA supports a wide range of bandwidths to flexibly address the need for various spectrum allocation and usage model requirements. The scalability of the OFDMA system is accomplished by adjusting the FFT size while fixing the sub-carrier frequency spacing at 10.94 kHz. Since the resource unit sub-carrier bandwidth and symbol duration is fixed, the impact to higher layers is minimal when scaling the bandwidth. A set of embodiments for S-OFDMA parameters are listed in TABLE 1 below.

TABLE 1
SCALABLE OFDMA PARAMETERS OF WIMAX
Parameters	Values
System Channel Bandwidth (MHz)	1.25	5	10	20
Sampling Frequency (Fp in MHz	1.4	5.6	11.2	22.4
FFT Size (NFFT)	128	512	1024	2048
Number of Subchannels	2	8	16	32
Sub-Carrier Frequency Spacing	10.94 kHz
Useful Symbol Time (Tb = 1/f)	91.4 microseconds
Guard Time (Tg = Tb/8)	11.4 microseconds
OFDMA Symbol Duration	102.9 microseconds
(Ts = Tb + Tg)
Number of OFDMA Symbols	48
(5 ms Frame)

FIGS. 5A and 5B depict exemplary distributed sub-carrier allocations 500a and 500b (sometimes collectively referred to herein as distributed sub-carrier allocation 500) associated with a particular Fourier fast transform (FFT) bin number according to one embodiment of the present disclosure. FIGS. 5A and 5B depict distributed sub-carrier allocations 500a and 500b in, for example, Cell ID 0 and Cell ID 1, respectively, and are referred to herein for illustration purposes only.

FIG. 5A illustrates four groups of subcarriers, groups 502a, 502b, 502c and 502d (collectively referred to herein as groups 502). Each of the subcarriers depicted in groups 502 are associated with a specific subchannel, subchannels 504a and 504b (collectively referred to herein as subchannels 504). Although only two subchannels 504 are shown in FIG. 5B, it should be understood that any suitable number of subchannels 504 may be apparent. Each of subchannels 504 generally includes forty-eight (48) data subcarriers.

Similarly, FIG. 5B illustrates four groups of subcarriers, groups 506a, 506b, 506c and 506d (collectively referred to herein as groups 506). Each of the subcarriers depicted in groups 506 are associated with a specific subchannel, subchannels 508a and 508b (collectively referred to herein as subchannels 508). Although only two subchannels 508 are shown in FIG. 5B, it should be understood that any suitable number of subchannels 508 may be apparent. Each of subchannels 508 generally includes forty-eight (48) data subcarriers.

FIG. 6 illustrates a WiMAX OFDM/OFDMA broadcast frame 600 for TDD implementation according to one embodiment of the present disclosure. Broadcast frame 600 illustrates the relationship between a given subchannel logical number 602 and a macrocell OFDM/OFDMA time slot or symbol number 604. Broadcast frame 600 is further divided into and supports subchannelization in DL subframe 606 and UL subframe 608. DL sub-frame 606 and UL subframe 608 are separated by transmit/receive transition gaps (TTG) and receive/transmit transition gaps (RTG) (collectively referred to herein as transition gap 610). Transition gap 610 prevents DL and UL transmission collisions. DL subframe 606 and UL subframe 608 include several unused or idle spectrum such as, for example, idle blocks 612, 614 and 616. Although a specified number of idle blocks is illustrated in DL subframe 606 and UL subframe 608, it should be understood that any suitable number of idle blocks could in fact be available in accordance with the present disclosure.

Control information for broadcast frame 600 is used to ensure optimal system operation. For example, control information may include preamble 618, frame control head (FCH) 620, DL-MAP 622, UL-MAPs 624a and 624b (collectively referred to herein as UL-MAP 624), UL ranging subchannel 626, UL channel quality indicator channel (CQICH) 628 and UL acknowledge subchannel (ACK) 630. Preamble 618 is used for synchronization of the first symbol number 604 of broadcast frame 600. FCH 620 follows preamble 618 and provides frame configuration information such as MAP message lengths, coding schemes and usable subchannels.

DL-MAP 622 and UL-MAP 624 provide subchannel allocation and other control information for DL subframe 606 and UL subframe 608, respectively. UL ranging subchannel 626 is allocated for mobile stations (MS) to perform closed-loop time, frequency, and power adjustment as well as bandwidth requests. UL CQICH 628 is allocated for the MS to feedback channel state information, while UL ACK 630 is allocated for the MS to feedback DL (hybrid automatic request) HARQ acknowledgement.

DL subframe 606 is shown with several DL data bursts 632a, 632b, 632c, 632d and 632e (sometimes collectively referred to herein as DL data bursts 632). It should be understood that any suitable number of DL data bursts 632 may be included in DL subframe 606. Similarly, UL subframe 608 is shown with several UL data bursts 634a, 634b, 634c, 634d and 634e) (sometimes collectively referred to herein as UL data bursts 634). It should be understood that any suitable number of UL data bursts 634 may be included in UL subframe 606.

FIGS. 7A and 7B depict exemplary broadcast frames 700a and 700b, respectively. Broadcast frames 700a and 700b are sometimes collectively referred to herein as broadcast frames 700. Broadcast frames 700 include DL subframe 702a, UL subframe 702b and many other elements similar to broadcast frame 600. According to one embodiment, broadcast frames 700 also include dedicated network subchannel 704a in the DL subframe 702a and dedicated network subchannel 704b in the UL subframe 702b. Dedicated network subchannel 704a and dedicated subchannel 704b are sometimes collectively referred to herein as dedicated subchannels 704.

In one embodiment, dedicated network subchannels 704 could occupy the entire subchannel or several subchannels within broadcast frames 700. In other embodiments, dedicated network subchannels 704 could occupy any part of a subchannel or multiple parts of several channels within broadcast frames 700. Preferably, dedicated network subchannels 704 are reserved for use by, for example, private networks, enterprise networks, premium service networks, a particular femtocell device or group of femtocell devices, a particular WiMAX cell or group of WiMAX cells, a small office/home office (SOHO) or group of SOHOs, a femtocell or group of femtocells, or any other network, subnetwork or other groups of devices requiring dedicated service to a particular set of users or groups of users. A separate subchannel (i.e., dedicated network subchannel 704) for the exclusive use of private network users minimizes interference with existing cellular services because the OFDMA subcarriers are orthogonal. Accordingly, embodiments of the present disclosure have many advantages over conventional CDMA or WCDMA systems.

Each of dedicated network subchannels 704 could be associated with a private user subframe or private user map (PU-MAP) 706 as described in detail later herein. PU-MAP 706 provides sub-channel allocation and other control information for at least one of dedicated network subchannel 704a and dedicated subchannel 704b. In other words, PU-MAP 706 identifies subcarriers (i.e. idle spectrum) that are available to members of a particular dedicated network. For example, PU-MAP 706 provides information on available subcarriers within broadcast frames 700, and more specifically, idle spectrum information associated with dedicated network subchannels 704. In one embodiment, PU-MAP 706 could identify available subcarriers by including a format similar to that shown in TABLE 2 below.

TABLE 2
EXEMPLARY PU-MAP FRAME FORMAT
Syntax	Size	Notes
PU_MAP( ) {
N_SLOTS	8 bits	The number of idle slots available in
		the frame.
For
(n=0;n<N_SLOTS;n++){
PERM_Indicator	1 bit	Indicates whether or not open slot ‘n’,
		as defined by the parameters below, is
		available in all future frames.
UL-DL Indicator	1 bit	Indicates whether open slot ‘n’ is in
		the Up Link Frame (‘0’) or the Down
		Link Frame (‘1’).
OFDMA Symbol	8 bits	The offset of the OFDMA symbol in which
Offset		slot n starts, measured in OFDMA
		symbols from the beginning of frame in
		which open slot ‘n’ is included (either
		UL or DL, depending on the UL-DL
		Indicator).
Subchannel Offset	6 bits	The lowest index OFDMA subchannel in
		open slot n, starting from subchannel
		‘0’
No. OFDMA Symbols	7 bits	The number of OFDMA symbols that make
		up open slot ‘n’.
No. Channels	6 bits	The number of subchannels, with
		subsequent indexes, that make up slot
		‘n’

The location of PU-MAP 706 within broadcast frame 700 could vary. For example, in one embodiment, PU-MAP 706 could be part of a reserved spectrum such as dedicated network subchannel 704a as shown in FIG. 7A. In other embodiments, PU-MAP 706 could be separate from dedicated network subchannel 704a and adjacent to UL-MAP 624 as shown in FIG. 7B. In still other embodiments, PU-MAP 706 could be located in any other suitable part of broadcast frames 700 accessible by secondary users or secondary nodes. In addition, PU-MAP 706 could occupy any suitable number of subchannels and/or symbol periods within a particular broadcast frame 700. In other embodiments, PU-MAP 706 could be located adjacent to DL-MAP 622. The location of PU-MAP 706 is, however, preferably known by members of a particular dedicated network and other specified secondary nodes. In one embodiment, a bit setting in FCH 620 or DL-MAP 622 could be used to indicate the presence of PU-MAP 706. It should be understood that other suitable methods of indicated the presence of PU-MAP 706 could also be used.

In one embodiment, for example, PU-MAP 706 identifies the groupings of carriers into one or more dedicated network subchannels 704. The format of dedicated network subchannels 704 identifies the dedicated network pilot subcarriers used for channel estimation by secondary nodes. PU MAP 706 preferably extracts idle spectrum information associated with at least one of the dedicated network subchannels 704 and provides that information to secondary nodes associated with the dedicated network.

Accordingly, PU-MAP 706 includes information accessible by members of a dedicated network to aid in transmitting and receiving data. For example, when a femtocell device associated with a WiMAX network is assigned a DL burst slot, the WiMAX BTS transmits PU-MAP 706 to the femtocell. The nodes associated with the dedicated network must know the CID of the femtocell device, so that the node can determine when to listen for the transmission of information associated with PU-MAP 706. The nodes provide their own local CIDs which is used by PU-MAP 706 to identify DL and UL burst slots or idle spectrum within dedicated network subchannels 704. Accordingly, the dedicated network nodes can transmit/receive burst in the identified slots.

FIG. 7C is another illustration of exemplary DL subframe 702a having idle spectrum blocks 708a, 708b and 708c (sometimes collectively referred to herein as idle spectrum blocks or secondary node bursts 708). According to one embodiment, each one of secondary user nodes 710a-710k (sometimes collectively referred to as secondary user nodes 710) shown in FIG. 7C could ascertain which set of subcarriers and symbol numbers 604 will be idle or unassigned during a given OFDM/OFDMA frame. For example, secondary nodes 710 could locate idle spectrum blocks 708 in dedicated network subchannel 704a during a given OFDM/OFDMA frame such as in broadcast frame 700. In other embodiments, secondary nodes 710 could locate idle spectrum in subchannels (other than dedicated network subchannel 704) found in broadcast frame 700 such as, for example, in idle block 612 or idle block 614.

In one embodiment, if one of secondary nodes 710 does not have data to transmit, that secondary node 710 listens for data symbols transmitted by neighboring secondary nodes 710 on idle subcarriers during the idle symbol periods (e.g., idle spectrum blocks 708). On the other hand, if one of secondary nodes 710 has data to transmit, that secondary node 710 transmits data transmitted to neighboring secondary nodes 710 on idle subcarriers during the idle symbol periods for the down-link (e.g., idle spectrum blocks 708). Transmission by the ad hoc or secondary nodes 710 within up-link idle spectrum is similarly accomplished.

Accordingly, in one embodiment, the present disclosure provides a system for providing ad hoc network users to share spectrum in networks that use OFDMA on a non-interfering or leasing basis. Dedicated subchannel 704 is preferably reserved for dedicated or private networks and should not be assignable to users that are not part of the ad hoc or dedicated network. The RF transmitter power of devices in the dedicated network should aid in limiting the size of the dedicated network coverage area.

In some embodiments, the base transceiver station could notify users of the dedicated network of the subcarriers reserved for the dedicated network in that particular cell. For example, the MAC processing block of a particular BTS could forward information about dedicated subchannel 704 to a node controller associated with a particular one of secondary nodes 710. To establish access to the OFDMA channel, that secondary node 710 detects the broadcast OFDMA waveform and synchronizes to the OFDMA frame to extract idle spectrum information using a frame detector.

Referring now to FIG. 8, the symbol period or length (T_x) of secondary node data bursts 708 is preferably kept less than or equal to in time duration as the OFDM symbol period (T_s) in broadcast frames 700. Secondary node data burst 708 may use a variable length symbol format. However, a shorter symbol period (T_x) implies a greater subcarrier spacing if the secondary node modulation is based on OFDM as well.

In one embodiment of the present disclosure, the secondary node 710 starts transmission after the passage of a guard time (T_g) such as in the ALOHA scheme shown in FIG. 8. In another embodiment of the present disclosure, the transmitting node determines if another secondary node 710 is already transmitting in unassigned subcarriers in symbol number 604 by conventional carrier sense multiple access (CSMA) techniques. As an example, secondary node 710c could transmit data in idle spectrum blocks 708a, while at the same time secondary node 710b could transmit data in idle spectrum blocks 708b. Moreover, two secondary nodes 710 may transmit simultaneously in the same symbol number 604 in different subcarriers. If unassigned subcarriers are found to be in use by other secondary nodes 710, other secondary nodes 710 waits for the next idle block (e.g., idle spectrum blocks 708a, 708b and 708c or, in some embodiments, idle block 612, 614 or 616) and repeats the access process.

In one embodiment, the battery life for battery-powered secondary nodes 710 could be extended. For example, secondary nodes 710 can power-down the transmitter circuitry of there is no data to transmit. Furthermore, secondary nodes 710 can power-down the receiver circuitry and other non-essential circuits during symbol number 604 when there are no idle subcarriers. The secondary nodes 710 power up at the appropriate time to receive, for example, broadcast frame 700, DL-MAP 622, UL-MAP 624 and PU-MAP 706.

FIG. 9 is a somewhat simplified flow diagram of method 900 for synchronous spectrum sharing based on OFDM/OFDMA signaling for a dedicated network subchannel such as, for example, dedicated network subchannel 704a, according to one embodiment of the present disclosure.

In step 905, a secondary user or secondary node, such as secondary node 710a, detects a broadcast OFDMA waveform. In step 910, an OFDM/OFDMA frame detector synchronizes the waveform to a broadcast frame, such as broadcast frame 700. In step 915, the frame detector extracts down-link and up-link channel assignments for that frame and identifies idle spectrum from a private user subframe or map (e.g., PU-MAP 706) associated with a dedicated network channel 704a. The idle spectrum information is then forwarded to a node modem associated with secondary node 710a in step 920.

Secondary node 710a thus gains dynamic access to dedicated network channel 704a using idle spectrum blocks 706 (i.e., “white space”) and can transmit data in the idle spectrum blocks 708 in a non-interfering or leasing basis in step 925. Accordingly, secondary users could dynamically form ad-hoc mesh network communications in fixed or mobile scenarios without interfering with agreements/etiquettes imposed by other users such as primary users and/or regulatory entities.

Although the present disclosure has been described with an exemplary embodiment, various changes and modifications may be suggested to one skilled in the art. It is intended that the present disclosure encompass such changes and modifications as fall within the scope of the appended claims.

Claims

1. A synchronous spectrum sharing system for use in a wireless communication system having a dedicated network subchannel associated with a broadcast frame, the system comprising: a frame detector configured to extract idle spectrum information for the dedicated network subchannel from a subframe within the broadcast frame,wherein a secondary node transmits data in a first unused symbol slot identified in the idle spectrum information.

2. The system set forth in claim 1, wherein the subframe comprises a portion of the dedicated network subchannel.

3. The system set forth in claim 1, wherein the subframe is associated with at least one of: a down-link subframe of the broadcast frame and an up-link subframe of the broadcast frame.

4. The system set forth in claim 1, wherein users of the dedicated network subchannel comprise a private network of secondary users.

5. The system set forth in claim 1, wherein the frame detector is one of: an OFDM frame detector and an OFDMA frame detector.

6. The system set forth in claim 1, wherein the broadcast frame is one of: an OFDM frame and an OFDMA frame.

7. The system set forth in claim 1, wherein a node modem associated with the secondary node and the frame detector are synchronized.

8. The system set forth in claim 1, wherein the secondary user node extracts a down-link channel assignment and an up-link channel assignment associated with the dedicated network subchannel.

9. The system set forth in claim 1, wherein a second secondary node transmits data in a second unused symbol slot identified in the idle spectrum information.

10. For use in a wireless communication network, a method of synchronous spectrum sharing comprising: detecting a subframe associated with a dedicated network subchannel from a broadcast waveform;extracting idle spectrum information for the dedicated network subchannel from the subframe; andtransmitting data in a first unused symbol slot identified in the idle spectrum information.

11. The method set forth in claim 10, wherein the subframe comprises a portion of the dedicated network subchannel.

12. The method set forth in claim 10, wherein users of the dedicated network subchannel comprise a private network of secondary users.

13. The method set forth in claim 10, wherein the detecting is accomplished by one of: an OFDM frame detector and an OFDMA frame detector.

14. The method set forth in claim 10, wherein the broadcast waveform is one of: an OFDM waveform and an OFDMA waveform.

15. The method set forth in claim 10 further comprising: extracting a down-link channel assignment and an up-link channel assignment for the dedicated network subchannel.

16. The method set forth in claim 10 further comprising: transmitting data from a second secondary node in a second unused symbol slot identified in the idle spectrum information.

17. For use in an OFDM/OFDMA wireless communication system, an apparatus for synchronous spectrum sharing, the apparatus comprising: a secondary node configured to extract idle spectrum information from a subframe associated with a dedicated network subchannel of a broadcast frame,wherein the secondary node transmits data in a first unused symbol slot identified in the idle spectrum information.

18. The apparatus set forth in claim 17, wherein the subframe comprises a portion of the dedicated network subchannel.

19. The apparatus set forth in claim 17, wherein the dedicated network subframe is associated with at least one of: a down-link subframe of the broadcast frame and an up-link subframe of the broadcast frame.

20. The apparatus set forth in claim 17, wherein users of the dedicated network subchannel comprises a private network of secondary users.

21. The apparatus set forth in claim 17, wherein the dedicated network subchannel comprises at least one of: an entire subchannel of the frame, a portion of a subchannel of the frame, and two or more subchannels of the frame.

22. The apparatus set forth in claim 17, wherein the secondary node extracts a down-link channel assignment and an up-link channel assignment for the dedicated network subchannel.

23. The apparatus set forth in claim 17, wherein a second secondary node transmits data in a second unused symbol slot identified in the idle spectrum information.