Survey of RF Communications and Sensing Convergence Research <s> F. TIME & POLARIZATION ORTHOGONALIZATION <s> We have designed, simulated, fabricated, and tested an ultra-wideband (UWB) multifunctional communication and radar system utilizing a single shared transmitting antenna aperture. Two surface acoustic wave bandpass chirp filters were used to modulate the radar and communications pulses, generating linear frequency modulation waveforms with opposite slope factors. The system operates at a center frequency of 750 MHz with 500 MHz of instantaneous bandwidth. The measured range resolution is 63 cm (25 in) using targets with a radar cross section of 2.7 m2. The probability of detection was measured to be 99%, and the probability of false alarm was 7% with the communication and radar systems operating simultaneously. The bit error rate for simultaneous communication at 1 Mb/s, and radar at 150 kHz pulse repetition frequency and 1.5-ns pulsewidth is 2e - 3. Our UWB multifunctional system demonstrates the ability to simultaneously interrogate the environment and communicate through a shared transmitting antenna aperture, while realizing a simple system architecture with low output power and not employing time-division multiplexing. <s> BIB001 </s> Survey of RF Communications and Sensing Convergence Research <s> F. TIME & POLARIZATION ORTHOGONALIZATION <s> Dynamic Frequency Selection (DFS) is the technology chosen by ETSI, FCC, and Industry Canada to provide unlicensed access for broadband radios in licensed bands. It is implemented by the basestation or basestation/subscriber combination. In a time-division duplexed (TDD) system with DFS implemented solely at the basestation, a periodic `quiet time' is enforced. This work determines the likelihood that a radar pulse train can be detected in a TDD system with radar detection restricted to the basestation. The results are tailored for TDD systems such as WiMAX, and can be used by designers to determine under what system constraints DFS can be implemented in their systems. <s> BIB002 </s> Survey of RF Communications and Sensing Convergence Research <s> F. TIME & POLARIZATION ORTHOGONALIZATION <s> This paper considers opportunistic primary-secondary spectrum sharing when the primary is a rotating radar. A secondary device is allowed to transmit when its resulting interference will not exceed the radar's tolerable level, in contrast to current approaches that prohibit secondary transmissions if radar signals are detected at any time. We consider the case where an OFDMA based secondary system operates in non-contiguous cells, as might occur with a broadband hotspot service, or a cellular system that uses spectrum shared with radar to supplement its dedicated spectrum. It is shown that even fairly close to a radar, extensive secondary transmissions are possible, although with some interruptions and fluctuations as the radar rotates. For example, at 27% of the distance at which secondary transmissions will not affect the radar, on average, the achievable secondary data rates in down- and upstreams are around 100% and 63% of the one that will be achieved in dedicated spectrum, respectively. Moreover, extensive secondary transmissions are still possible even at different values of key system parameters, including cell radius, transmit power, tolerable interference level, and radar rotating period. By evaluating quality of service, it is found that spectrum shared with radar could be used efficiently for applications such as non-interactive video on demand, peer-to-peer file sharing, file transfers, automatic meter reading, and web browsing, but not for applications such as real-time transfers of small files and VoIP. <s> BIB003 </s> Survey of RF Communications and Sensing Convergence Research <s> F. TIME & POLARIZATION ORTHOGONALIZATION <s> This paper considers gray-space spectrum sharing when rotating radars are primary spectrum users, and multiple cells from one or more cellular networks are secondary users. A cellular network may share spectrum to supplement its dedicated spectrum, or provide a broadband hotspot service. A secondary device is allowed to transmit as long as cumulative interference is not harmful to nearby radars, probably because no radar is pointing its directional antenna at the device at this moment. This paper presents mechanisms that would support such sharing, and quantifies performance when spectrum is considered 100% utilized under traditional spectrum management. It is shown that the sharing allows cells to sustain significant mean data rates. For example, if 5% of a cellular network's cells need more capacity than dedicated spectrum can provide, a cell can get almost 1.2 bps/Hz on average from shared spectrum. By evaluating quality of service, it is found that shared spectrum could be used efficiently for applications such as non-interactive video streaming, peer-to-peer file sharing, large file transfers, and web browsing, but not for applications such as real-time transfers of small files, and VoIP. <s> BIB004 </s> Survey of RF Communications and Sensing Convergence Research <s> F. TIME & POLARIZATION ORTHOGONALIZATION <s> Databases have been considered in the context of spectrum sharing systems to collect information on spectrum usage by primary users and to provide information on spectrum opportunities to secondary users. We develop a database-aided distributed channel assignment protocol (CAP) for secondary access control in a spectrum sharing system. Based upon a slotted, multichannel random access system model, we describe several secondary CAPs with varying levels of information from the database. We analyze handshake performance within a single slot based upon a given number of secondary users and a limited number of available channels, and we study the system transient performance for reaching steady state. System throughput and delay are also derived based on the number of secondary users and available channels. Finally, we propose dynamic channelization within the system bandwidth based upon the number of secondary users to maximize throughput. <s> BIB005 </s> Survey of RF Communications and Sensing Convergence Research <s> F. TIME & POLARIZATION ORTHOGONALIZATION <s> The approach to spectrum sharing explored in this paper is based on unilateral action by Wi-Fi networks to prevent unacceptable interference to incumbent search radars (e.g., those operating in S-band). Specifically, we evaluate the ability of a single Wi-Fi network to speedily detect radar operation and to subsequently switch to a clear channel as a means of protecting them. We rely on the opportunistic use of naturally occurring random quiet/idle periods in a Wi-Fi network employing distributed coordination function to detect the presence of a radar using energy detection. We analytically characterize the statistical properties of the idle periods in terms of occurrence and duration in the full buffer and downlink only traffic cases, and verify our analysis using simulations. We then suggest simple modifications to Wi-Fi parameters in order to improve radar detection performance and examine the resulting Wi-Fi throughput costs. The key contribution of this paper is to thoroughly characterize the Wi-Fi throughput versus detection tradeoff implicated by this coexistence mechanism. <s> BIB006
Other methods of isolation include polarization BIB001 for co-designed systems, where a radar transceiver is on an orthogonal polarization axis relative to the communications receiver, though no performance with respect to isolation is given. Space-time dynamic isolation techniques have also been proposed, such as communications devices dutycycling carefully to avoid spectral collisions with rotating radars BIB003 - BIB004 assuming knowledge of how the radar is transmitting as a function of time. In the absence of this knowledge, researchers have investigated dynamic communications schemes employing electronic intelligence (ELINT) techniques to augment knowledge aided databases and avoid active radar transmitting interference  , BIB005 . As a means to combat radar interference in Wi-Fi systems, some have investigated detecting radar during Wi-Fi quiet times as a means to mitigate the radar signal within the Wi-Fi framework by switching to an interference-free channel BIB006 . A similar system detects radar pulse trains during quiet time and applies this knowledge to time-division duplexing (TDD) systems like WiMAX BIB002 .