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...n the operation in the TV white spaces. The remaining are recently published ECMA TC48-TG1 standard [12] focusing on porting local area networks to TV white spaces, and recently started IEEE 802.11af =-=[13]-=-, similar in scope to the aforementioned ECMA activity. 3allows the investigation of interactions between medium access control and spectrum sensing layer. Since many options of OS-OFDMA subcarrier an...

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...ested for the IEEE 802.22. We name this strategy channel blocking and denote it symbolically as N0. Please note that channel switching delays is in the order of tens to hundreds of microseconds [60], =-=[61]-=- which is a fraction of the channel sensing time. Dependent on protocol design, an additional OFDMA frame might be needed to communicate the decision about channel switch between base station and term...

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...tural to connect the strengths of OFDMA with the flexibility of OSA. The first paper that introduced such concept, denoted in the reminder of this paper as Opportunistic Spectrum OFDMA (OS-OFDMA) was =-=[7]-=- (referred therein as Spectrum Pooling) where OFDM subcarriers assigned to individual OSA users (denoted as Secondary Users (SUs)) are deactivated whenever the Primary User (PU) of the radio frequency...

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...ilable at http://arxiv.org/abs/1007.5080. 2I. INTRODUCTION One of the ways to combat artificial spectrum scarcity [2] is to augment existing radio access techniques with Opportunistic Spectrum Access =-=[3]-=- (OSA). Wireless networks with OSA capabilities are able to search for unused licensed portions of the radio spectrum and communicate over those vacant radio frequencies whenever available radio capac...

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...nd cross-layer performance of OS-OFDMA networks has been reported. The need for theoretical framework for OS-OFDMA is also motivated by the recent introduction of OSA network standard IEEE 802.22 [9]–=-=[11]-=-. The IEEE 802.22, an extension of the IEEE 802.16 standard, is designed to operate in the vacant TV bands1. In the application domain the IEEE 802.22 has already been proposed to bridge remote wirele...

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...llow the same path. Note, however, that the proposed model is extendable to the case where PU slots are offset in time from SU slots. This would require further analysis of PU channel access policies =-=[44]-=-, [45] which is beyond the scope of this paper. We emphasize, as in [35], [46], that assumption about the synchrony between PU and SU connections allows to calculate throughput upper bounds compared t...

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...eters for the spectrum sensing PHY are the probability of detection, the probability of false alarm and the sensing time. There is a trade-off between the sensing time and the resulting probabilities =-=[49]-=-. That is, if a SU takes a long time to sense a subchannel, the time for data transmission may be reduced. However, more idle subchannels can be detected because of high accuracy, which in turn may in...

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...of the considered location, while the wireless microphones move in and out of the BS circular coverage with a certain speed v = 1.5mph (for all scenarios). Then using a fluid flow model approximation =-=[63]-=- we compute the average crossing rate of the wireless microphones to that area and translate it directly to an average arrival rate of wireless microphone on any of the subchannels. That is λn = ρhpiL...

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...sensing mechanisms were included in the model. Finally, we need to mention a set of papers analyzing performance of medium access control protocols for OSA networks. Some of the relevant ones include =-=[32]-=-–[35], however none of those works consider 4Transport/Network/Application Data MAC Data PHY SS MAC Subchannel Notching Channel Bonding (Channels, Subchannels) OFDMA configuration Multi-Stage SS False...

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... as well as robustness against inter-symbol interference, OFDMA was a design choice of recent wireless networking standards, e.g. the IEEE 802.16 [4], the IEEE 802.20 [5] and 3GPP Long Term Evolution =-=[6]-=-. As opportunistic spectrum use can be implemented efficiently with OFDMA, it seemed natural to connect the strengths of OFDMA with the flexibility of OSA. The first paper that introduced such concept...

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...hed in the proceedings of IEEE GLOBECOM, Dec. 6–10, 2010, Miami, FL, USA [1]. Also available at http://arxiv.org/abs/1007.5080. 2I. INTRODUCTION One of the ways to combat artificial spectrum scarcity =-=[2]-=- is to augment existing radio access techniques with Opportunistic Spectrum Access [3] (OSA). Wireless networks with OSA capabilities are able to search for unused licensed portions of the radio spect...

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...he same path. Note, however, that the proposed model is extendable to the case where PU slots are offset in time from SU slots. This would require further analysis of PU channel access policies [44], =-=[45]-=- which is beyond the scope of this paper. We emphasize, as in [35], [46], that assumption about the synchrony between PU and SU connections allows to calculate throughput upper bounds compared to tran...

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...ual OSA users (denoted as Secondary Users (SUs)) are deactivated whenever the Primary User (PU) of the radio frequency band reappears. For a recent discussion on the topic of OS-OFDMA please refer to =-=[8]-=-. So far no theoretical work on the system-level and cross-layer performance of OS-OFDMA networks has been reported. The need for theoretical framework for OS-OFDMA is also motivated by the recent int...

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...ce analysis studies [47]. The analysis can be extended to the general distributions of PU and SU traffic, which is beyond the scope 7of this paper. Note, however, that the recent measurement campaign =-=[48]-=- showed that more than 60% of measured PU activities distributions, including ISM and cellular bands, fitted an exponential distribution. The average inter-arrival and departure time are denoted, resp...

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... MIMO extensions for the IEEE 802.22 physical layer [21], game theoretic analysis of the the IEEE 802.22 networks coexistence [22]–[25], [26], [27] (with joint resource allocation), duplexing schemes =-=[28]-=- (frequency hopping operation), [15] (time division duplex design), and mesh establishment [29], it is desirable to develop unifying model that captures the IEEE 802.22 intrinsic features such as mult...

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... generate new connections according to the negative exponential distribution for the inter-arrival time and burst departure time, which is again a classical assumption in performance analysis studies =-=[47]-=-. The analysis can be extended to the general distributions of PU and SU traffic, which is beyond the scope 7of this paper. Note, however, that the recent measurement campaign [48] showed that more th...

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...s suggested for the IEEE 802.22. We name this strategy channel blocking and denote it symbolically as N0. Please note that channel switching delays is in the order of tens to hundreds of microseconds =-=[60]-=-, [61] which is a fraction of the channel sensing time. Dependent on protocol design, an additional OFDMA frame might be needed to communicate the decision about channel switch between base station an...

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...esign [18], [19], circuit design for dedicated spectrum sensing [20], MIMO extensions for the IEEE 802.22 physical layer [21], game theoretic analysis of the the IEEE 802.22 networks coexistence [22]–=-=[25]-=-, [26], [27] (with joint resource allocation), duplexing schemes [28] (frequency hopping operation), [15] (time division duplex design), and mesh establishment [29], it is desirable to develop unifyin...

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...thm design [18], [19], circuit design for dedicated spectrum sensing [20], MIMO extensions for the IEEE 802.22 physical layer [21], game theoretic analysis of the the IEEE 802.22 networks coexistence =-=[22]-=-–[25], [26], [27] (with joint resource allocation), duplexing schemes [28] (frequency hopping operation), [15] (time division duplex design), and mesh establishment [29], it is desirable to develop un...

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...s, like [50] where quite-active sensing is proposed with non-active users sensing while others actively communicating, since they belong to a single-stage spectrum sensing category. 8context refer to =-=[51]-=-–[53] for two-stage sensing multi-channel system, and [54] for two-stage sensing single channel system. In this work we limit ourselves to two-stage sensing, noting that our analysis can be directly e...

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...ptions, has been presented. Focusing on the IEEE 802.22, interestingly, while many papers analyzed a certain functionality of the IEEE 802.22 network, like efficient spectrum sensing algorithm design =-=[18]-=-, [19], circuit design for dedicated spectrum sensing [20], MIMO extensions for the IEEE 802.22 physical layer [21], game theoretic analysis of the the IEEE 802.22 networks coexistence [22]–[25], [26]...

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...ng mechanisms were included in the model. Finally, we need to mention a set of papers analyzing performance of medium access control protocols for OSA networks. Some of the relevant ones include [32]–=-=[35]-=-, however none of those works consider 4Transport/Network/Application Data MAC Data PHY SS MAC Subchannel Notching Channel Bonding (Channels, Subchannels) OFDMA configuration Multi-Stage SS False alar...

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...el and cross-layer performance of OS-OFDMA networks has been reported. The need for theoretical framework for OS-OFDMA is also motivated by the recent introduction of OSA network standard IEEE 802.22 =-=[9]-=-–[11]. The IEEE 802.22, an extension of the IEEE 802.16 standard, is designed to operate in the vacant TV bands1. In the application domain the IEEE 802.22 has already been proposed to bridge remote w...

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...-OFDMA, which 1Note that the IEEE 802.22 is not the only networking standard proposed that focused on the operation in the TV white spaces. The remaining are recently published ECMA TC48-TG1 standard =-=[12]-=- focusing on porting local area networks to TV white spaces, and recently started IEEE 802.11af [13], similar in scope to the aforementioned ECMA activity. 3allows the investigation of interactions be...

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...e case where PU slots are offset in time from SU slots. This would require further analysis of PU channel access policies [44], [45] which is beyond the scope of this paper. We emphasize, as in [35], =-=[46]-=-, that assumption about the synchrony between PU and SU connections allows to calculate throughput upper bounds compared to transmission on a slot-asynchronous interface. Furthermore, we assume that e...

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...on-active users sensing while others actively communicating, since they belong to a single-stage spectrum sensing category. 8context refer to [51]–[53] for two-stage sensing multi-channel system, and =-=[54]-=- for two-stage sensing single channel system. In this work we limit ourselves to two-stage sensing, noting that our analysis can be directly extended to multi-stage sensing. The procedure works as fol...

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...ause of high spectral efficiency, as well as robustness against inter-symbol interference, OFDMA was a design choice of recent wireless networking standards, e.g. the IEEE 802.16 [4], the IEEE 802.20 =-=[5]-=- and 3GPP Long Term Evolution [6]. As opportunistic spectrum use can be implemented efficiently with OFDMA, it seemed natural to connect the strengths of OFDMA with the flexibility of OSA. The first p...

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...[18], [19], circuit design for dedicated spectrum sensing [20], MIMO extensions for the IEEE 802.22 physical layer [21], game theoretic analysis of the the IEEE 802.22 networks coexistence [22]–[25], =-=[26]-=-, [27] (with joint resource allocation), duplexing schemes [28] (frequency hopping operation), [15] (time division duplex design), and mesh establishment [29], it is desirable to develop unifying mode...

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...Table I. Note, that all options except S0N1B1, are considered by the IEEE 802.22 standard. 3Please refer to a recent studies on that topic that prove the feasibility of such approach. For example, in =-=[57]-=- a sidelobe suppression with guard band equal to only one OFDM subcarrier interval was shown. In [58] a OFDM subcarrier notching was proposed with only 4% of the available spectrum wastage. Finally a ...

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...band. Since in general, the traffic pattern of PUs for such case is not well known (more discussion on this aspect is presented in Section IV-C), for the WPU we keep the wireless assist video devices =-=[62]-=- in mind, which can be assumed to broadcast on average four hours of signal transmission for every twelve hours on average in this scenario. For the NPU, we consider environment with numerous wireless...

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... bands1. In the application domain the IEEE 802.22 has already been proposed to bridge remote wireless sensor networks with the command center [14] or support Internet connectivity in the rural areas =-=[15]-=-. Our goal is to develop the analytical framework to analyze the impact of traffic characteristics of OS-OFDMA network subscribers, the activity of the PUs of the radio spectrum, as well as the spectr...

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...[19], circuit design for dedicated spectrum sensing [20], MIMO extensions for the IEEE 802.22 physical layer [21], game theoretic analysis of the the IEEE 802.22 networks coexistence [22]–[25], [26], =-=[27]-=- (with joint resource allocation), duplexing schemes [28] (frequency hopping operation), [15] (time division duplex design), and mesh establishment [29], it is desirable to develop unifying model that...

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...lasses of traffic, two stage spectrum sensing, different types of PUs and their temporal activity, and OFDMA subcarrier allocation process. The work closest to the scope of this paper can be found in =-=[30]-=- in which the IEEE 802.16 system was evaluated. Obviously the model developed therein cannot be used directly to evaluate OS-OFDMA system due to the lack of spectrum sensing and PUs activity features....

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...ity, as it is a well established and classical assumption in the theoretical analysis, see for example recent publications of [35], [36, Fig. 2], [33, Sec. III], [37, Fig. 1], [38, Fig. 2] [31], [39]–=-=[43]-=- that follow the same path. Note, however, that the proposed model is extendable to the case where PU slots are offset in time from SU slots. This would require further analysis of PU channel access p...

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...icity that it is possible to notch out subchannels and transmit on the adjacent subchannels without causing interference, which is a common assumption in system level analysis, e.g. [31], [40], [41], =-=[56]-=-3. On the opposite side, a conservative strategy is to exclude (block) all subchannels within the operating channel from accessing, even though only one subchannel is utilized by the PU, which is sugg...

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...rophone per 1000 EU inhabitants (assuming a constant level of wireless microphone shipments per year). Note that the value of 35,000–70,000 licensed wireless microphone operations in USA presented in =-=[65]-=- was not substantiated with any reference. 23 TABLE II SCENARIOS FOR THE ANALYSIS OF NPU ACTIVITY IMPACT ON THE PERFORMANCE OF OS-OFDMA DESIGNS Nickname “heavy urban” “urban” “light urban” “event” Loc...

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...nterestingly, while many papers analyzed a certain functionality of the IEEE 802.22 network, like efficient spectrum sensing algorithm design [18], [19], circuit design for dedicated spectrum sensing =-=[20]-=-, MIMO extensions for the IEEE 802.22 physical layer [21], game theoretic analysis of the the IEEE 802.22 networks coexistence [22]–[25], [26], [27] (with joint resource allocation), duplexing schemes...

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...activity, as it is a well established and classical assumption in the theoretical analysis, see for example recent publications of [35], [36, Fig. 2], [33, Sec. III], [37, Fig. 1], [38, Fig. 2] [31], =-=[39]-=-–[43] that follow the same path. Note, however, that the proposed model is extendable to the case where PU slots are offset in time from SU slots. This would require further analysis of PU channel acc...

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...fer to a recent studies on that topic that prove the feasibility of such approach. For example, in [57] a sidelobe suppression with guard band equal to only one OFDM subcarrier interval was shown. In =-=[58]-=- a OFDM subcarrier notching was proposed with only 4% of the available spectrum wastage. Finally a practical implementation of OFDM subcarrier suppression with perfect channel utilization at the cost ...

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... 802.16 standard, is designed to operate in the vacant TV bands1. In the application domain the IEEE 802.22 has already been proposed to bridge remote wireless sensor networks with the command center =-=[14]-=- or support Internet connectivity in the rural areas [15]. Our goal is to develop the analytical framework to analyze the impact of traffic characteristics of OS-OFDMA network subscribers, the activit...

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... lack of spectrum sensing and PUs activity features. A work similar in our scope (analyzing the system level aspects of subchannel/subcarrier allocation strategies for OS-OFDMA) has been presented in =-=[31]-=-. However, no comparison with the the IEEE 802.22 subchannel assignment has been considered. Furthermore, no QoS classes, PU priorities and two-stage spectrum sensing mechanisms were included in the m...

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...aper, we focus mostly on multi-stage sensing2. For the first results of multi-stage spectrum sensing in network 2We do not focus on recently proposed spectrum sensing methods for OFDMA networks, like =-=[50]-=- where quite-active sensing is proposed with non-active users sensing while others actively communicating, since they belong to a single-stage spectrum sensing category. 8context refer to [51]–[53] fo...

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...h only 4% of the available spectrum wastage. Finally a practical implementation of OFDM subcarrier suppression with perfect channel utilization at the cost of throughput reduction was demonstrated in =-=[59]-=-. 10 TABLE I SUMMARY OF DESIGN OPTIONS OF CONSIDERED IN THE PAPER Symbol Two-Stage Sensing Notching/Blocking Bonding/Separation S0N1B1 General Subchannel Notching Subchannel Bonding S0N0B1 General Cha...

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...individual users. Because of high spectral efficiency, as well as robustness against inter-symbol interference, OFDMA was a design choice of recent wireless networking standards, e.g. the IEEE 802.16 =-=[4]-=-, the IEEE 802.20 [5] and 3GPP Long Term Evolution [6]. As opportunistic spectrum use can be implemented efficiently with OFDMA, it seemed natural to connect the strengths of OFDMA with the flexibilit...

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...onality of the IEEE 802.22 network, like efficient spectrum sensing algorithm design [18], [19], circuit design for dedicated spectrum sensing [20], MIMO extensions for the IEEE 802.22 physical layer =-=[21]-=-, game theoretic analysis of the the IEEE 802.22 networks coexistence [22]–[25], [26], [27] (with joint resource allocation), duplexing schemes [28] (frequency hopping operation), [15] (time division ...

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...me for simplicity that it is possible to notch out subchannels and transmit on the adjacent subchannels without causing interference, which is a common assumption in system level analysis, e.g. [31], =-=[40]-=-, [41], [56]3. On the opposite side, a conservative strategy is to exclude (block) all subchannels within the operating channel from accessing, even though only one subchannel is utilized by the PU, w...

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... simplicity that it is possible to notch out subchannels and transmit on the adjacent subchannels without causing interference, which is a common assumption in system level analysis, e.g. [31], [40], =-=[41]-=-, [56]3. On the opposite side, a conservative strategy is to exclude (block) all subchannels within the operating channel from accessing, even though only one subchannel is utilized by the PU, which i...

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...ke [50] where quite-active sensing is proposed with non-active users sensing while others actively communicating, since they belong to a single-stage spectrum sensing category. 8context refer to [51]–=-=[53]-=- for two-stage sensing multi-channel system, and [54] for two-stage sensing single channel system. In this work we limit ourselves to two-stage sensing, noting that our analysis can be directly extend...

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...ormatics, University of Oslo, Gaustadallen 23, 0373 Oslo, Norway (email: paalrgr@ifi.uio.no). Part of this work has been published in the proceedings of IEEE GLOBECOM, Dec. 6–10, 2010, Miami, FL, USA =-=[1]-=-. Also available at http://arxiv.org/abs/1007.5080. 2I. INTRODUCTION One of the ways to combat artificial spectrum scarcity [2] is to augment existing radio access techniques with Opportunistic Spectr...

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...uch as number and type of primary users, the number and type of QoS classes enabled by OS-OFDMA network and the priority order in channel access for each class of users). Considering related work, in =-=[16]-=- a general framework of the IEEE 802.16 with OSA capabilities has been proposed with a very simplified networking model, based on Erlang-B formula [16, Sec. VA], where the focus of the paper has been ...

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...fied networking model, based on Erlang-B formula [16, Sec. VA], where the focus of the paper has been mostly on propagation calculations, including coverage, interference and protection distances. In =-=[17]-=- a simulation platform for the IEEE 802.22-like network, with limited set of ODFMA design options, has been presented. Focusing on the IEEE 802.22, interestingly, while many papers analyzed a certain ...

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..., has been presented. Focusing on the IEEE 802.22, interestingly, while many papers analyzed a certain functionality of the IEEE 802.22 network, like efficient spectrum sensing algorithm design [18], =-=[19]-=-, circuit design for dedicated spectrum sensing [20], MIMO extensions for the IEEE 802.22 physical layer [21], game theoretic analysis of the the IEEE 802.22 networks coexistence [22]–[25], [26], [27]...

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...EE 802.22 networks coexistence [22]–[25], [26], [27] (with joint resource allocation), duplexing schemes [28] (frequency hopping operation), [15] (time division duplex design), and mesh establishment =-=[29]-=-, it is desirable to develop unifying model that captures the IEEE 802.22 intrinsic features such as multiple classes of traffic, two stage spectrum sensing, different types of PUs and their temporal ...

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...is low. However, it is inefficient because some available bandwidth may not be utilized. Since it is one of the operating modes of the IEEE 802.22, also advocated by Federal Communications Commission =-=[55]-=-, we also include it in our study. We name this strategy fixed channel selection and denote it symbolically as B0. Secondly, we also need a strategy to avoid utilizing the subchannels on which the PU ...