共查询到20条相似文献,搜索用时 78 毫秒
1.
Chizhik D. Ling J. Wolniansky P.W. Valenzuela R.A. Costa N. Huber K. 《Selected Areas in Communications, IEEE Journal on》2003,21(3):321-331
Narrowband multiple-input-multiple-output (MIMO) measurements using 16 transmitters and 16 receivers at 2.11 GHz were carried out in Manhattan. High capacities were found for full, as well as smaller array configurations, all within 80% of the fully scattering channel capacity. Correlation model parameters are derived from data. Spatial MIMO channel capacity statistics are found to be well represented by the separate transmitter and receiver correlation matrices, with a median relative error in capacity of 3%, in contrast with the 18% median relative error observed by assuming the antennas to be uncorrelated. A reduced parameter model, consisting of 4 parameters, has been developed to statistically represent the channel correlation matrices. These correlation matrices are, in turn, used to generate H matrices with capacities that are consistent within a few percent of those measured in New York. The spatial channel model reported allows simulations of H matrices for arbitrary antenna configurations. These channel matrices may be used to test receiver algorithms in system performance studies. These results may also be used for antenna array design, as the decay of mobile antenna correlation with antenna separation has been reported here. An important finding for the base transmitter array was that the antennas were largely uncorrelated even at antenna separations as small as two wavelengths. 相似文献
2.
Razavilar J. Rashid-Farrokhi F. Liu K.J.R. 《Selected Areas in Communications, IEEE Journal on》1999,17(4):662-676
There has been considerable interest in using antenna arrays in wireless communication networks to increase the capacity and decrease the cochannel interference. Adaptive beamforming with smart antennas at the receiver increases the carrier-to-interference ratio (CIR) in a wireless link. This paper considers a wireless network with beamforming capabilities at the receiver which allows two or more transmitters to share the same channel to communicate with the base station. The concrete computational complexity and algorithm structure of a base station are considered in terms of a software radio system model, initially with an omnidirectional antenna. The software radio computational model is then expanded to characterize a network with smart antennas. The application of the software radio smart antenna is demonstrated through two examples. First, traffic improvement in a network with a smart antenna is considered, and the implementation of a hand-off algorithm in the software radio is presented. The blocking probabilities of the calls and total carried traffic in the system under different traffic policies are derived. The analytical and numerical results show that adaptive beamforming at the receiver reduces the probability of blocking and forced termination of the calls and increases the total carried traffic in the system. Then, a joint beamforming and power control algorithm is implemented in a software radio smart antenna in a CDMA network. This shows that, by using smart antennas, each user can transmit with much lower power, and therefore the system capacity increases significantly 相似文献
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A wireless interconnect system which transmits and receives RF signals across a chip using integrated antennas, receivers, and transmitters is proposed and demonstrated. The transmitter consists of a voltage-controlled oscillator, an output amplifier, and an antenna, while the receiver consists of an antenna, a low-noise amplifier, a frequency divider, and buffers. Using a 0.18-μm CMOS technology, each of these individual circuits is demonstrated at 15 GHz. Wireless interconnection for clock distribution is then demonstrated in two stages. First, a wireless transmitter with integrated antenna generates and broadcasts a 15-GHz global clock signal across a 5.6-mm test chip, and this signal is detected using receiving antennas. Second, a wireless clock receiver with an integrated antenna detects a 15-GHz global clock signal supplied to an on-chip transmitting antenna located 5.6 mm away from the receiver, and generates a 1.875-GHz local clock signal. This is the first known demonstration of an on-chip clock transmitter with an integrated antenna and the second demonstration of a clock receiver with an integrated antenna, where the receiver's frequency and interconnection distance have approximately been doubled over previous results 相似文献
5.
Göran Malmgren 《Wireless Personal Communications》1995,2(4):307-319
A receiver in an ODFM based broadcasting system allows all transmitters in a radio network to simultaneously broadcast the same information in the same frequency block. This procedure generates an artificial multipath environment at the receiver. Since the receiver is designed to overcome these problems, such a Single Frequency Network (SFN) provides good coverage and frequency economy in national applications. However, the efficiency in local SFN has been questioned. The network planning of local SFNs is a mixture of conventional frequency reuse planning and planning to avoid excessive propagation delays caused by the artificial delay spread. In this paper we propose some rules of thumb to be considered in the design of local SFNs. The coverage properties in SFNs are strongly dependent on the transmitter density which determines the degree of diversity of receiving signals from several transmitters. Results indicate that required coverage can be attained in local networks using three OFDM frequency blocks, provided that seven transmitters are used to cover each regional service area. The results also indicate that the duration of the guard interval between two consecutive OFDM signals has to be chosen with some care dependent on the size of the service area. Furthermore, we show that there exists an optimal antenna height for a given coverage area and guard interval. 相似文献
6.
《IEEE transactions on circuits and systems. I, Regular papers》2009,56(6):1173-1181
7.
Measurement of Layer Thickness and Permittivity Using a New Multilayer Model From GPR Data 总被引:1,自引:0,他引:1
Chien-Ping Kao Jing Li Ying Wang Huichun Xing Ce Richard Liu 《Geoscience and Remote Sensing, IEEE Transactions on》2007,45(8):2463-2470
The conventional method, i.e., the common middle point (CMP) method, has been used for many years for estimating the depth and permittivity of layered media from ground-penetrating radar (GPR) data. However, the CMP method results in noticeable errors in thickness and permittivity readings with the increase of antenna separation. To improve the measurement accuracy, a new mathematical model is presented, covering GPR measurement in one- and two-layer cases. In this model, we first check all the possible wave paths when the GPR signal propagates in the multilayer environment. We not only consider the effects from the air-ground interface but also introduce a ray-path-searching process in the GPR measurement using Fermat's shortest path law. The shortest path is then used in the process of GPR data inversion in order to calculate the depth and permittivity of each layer. Finally, we use the transmission-line matrix (TLM) method to simulate the propagation of a GPR signal in the multilayered formation. A time-sequence image that was produced by the finite-difference time-domain method has also been used to explain this presented model. By comparing the numerical simulation results with the measured results, it is found that the estimated layer thickness and permittivity by the new model agree well with the simulated results. It proves that the new model is more accurate and closer to the real measured situation. 相似文献
8.
This paper describes a simple delay diversity technique for terrestrial digital multimedia broadcasting (T‐DMB) and digital audio broadcasting in a single‐frequency network (SFN). For the diversity technique, a delay diversity scheme is adopted. In the delay diversity scheme, a non‐delayed signal is transmitted in the first antenna, and delayed versions of the signal are transmitted in each additional antenna. For an SFN environment with multiple transmitters, delay diversity can be executed by controlling the emission times of the transmitters. This SFN delay diversity scheme does not require any hardware changes in either the transmitter or receiver, and perfect backward compatibility can be acquired. To evaluate the performance improvement, laboratory tests are executed with various types of commercial T‐DMB receivers as well as a measurement receiver. The improvement in the bit error rate performance is evaluated using a measurement receiver, and an improvement of the threshold of visibility value is evaluated for commercial receivers. Test results show that the T‐DMB system can obtain diversity gain using the described technique. 相似文献
9.
《Vehicular Technology, IEEE Transactions on》1978,27(4):239-243
It has generally been accepted that in a two-branch diversity receiver a near maximum diversity advantage is realized when the cross correlation between the two branches is less than 0.7. Based on this figure, space diversity reception at the mobile presents little problem since the antenna separation distances that achieve this mount of decorrelation in the mobile environment are very small (≤20 cm at 850 MHz). However, the space diversity antenna separation requirement at the land site necessary to achieve the same amount of signal decorrelation is in the range of 10 wavelengths or more at antenna elevations of 150 ft or greater. Therefore, a comprehensive characterization of the effect of changing the cross correlation between the two received signals at the land site is important to effective system design. The performance of the two-branch equal-gain diversity system as a function of the cross-correlation between the two received signals from the diversity antennas is described. The cumulative probability distribution, level crossing rates, and duration of fades from a two-branch equal-gain combined diversity signal with variable correlation between the two branches are described also. 相似文献
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This paper studies the asymptotic performance of a multiple-input multiple-output (MIMO) multiple-access (MA) wireless network where spatial correlations at both the transmitters (i.e., mobile stations) and the central receiver (i.e., base station) exist, and more than one multiantenna sets are employed at the receiver to provide macrodiversity. The sense of asymptotic behavior we consider is the large-system limit in which the numbers of antennas at each mobile station and antenna set go to infinity with their ratios fixed. Using the replica method, we derive analytical solutions to the asymptotic spectral efficiency (SE) of the MIMO-MA systems for any given input distributions (not necessarily Gaussian) from the mobile transmitters. Our results can be regarded as the generalization of many previously known results for degenerate cases. Another contribution of this paper is an efficient algorithm to determine the asymptotic optimum transmit-signal covariance matrices that can maximize the SE of the MIMO-MA network within the period in which the spatial channel covariance information (CCI) can be considered static, and assuming that only CCI is available at the transmitters 相似文献
12.
Self-survey calibration of meteor radar antenna arrays 总被引:1,自引:0,他引:1
Valentic T.A. Avery J.P. Avery S.K. Livingston R.C. 《Geoscience and Remote Sensing, IEEE Transactions on》1997,35(3):524-531
This paper presents the self-surveying technique for calibrating the antenna spacing, orientation, and phase errors in multiple receiver radar antenna arrays. Utilizing a set of source transmitters placed at known locations in the far-field of the array and measurements of the phase present at each antenna, the array's relative antenna locations and phase errors can be determined. The advantage of this technique is that the radar is used in its normal operating mode, providing an end-to-end calibration under true operational conditions. A self-survey calibration was performed with a meteor radar located at Sondre Stromfjord, Greenland, successfully mapping the array. The antenna positions were relatively close the expected locations, although the baselines were rotated approximately 5° from the true cardinal directions. The majority of the phase error was introduced by the receivers 相似文献
13.
In this paper, we analyze the tradeoff between outage probability (OP) and intercept probability (IP) for a multi‐hop relaying scheme in cognitive radio (CR) networks. In the proposed protocol, a multi‐antenna primary transmitter (PT) communicates with a multi‐antenna primary receiver (PR), using transmit antenna selection (TAS) / selection combining (SC) technique, while a secondary source attempts to transmit its data to a secondary destination via a multi‐hop approach in presence of a secondary eavesdropper. The secondary transmitters such as source and relays have to adjust their transmit power to satisfy total interference constraint given by PR. We consider an asymmetric fading channel model, where the secondary channels are Rician fading, while the remaining ones experience the Rayleigh fading. Moreover, an optimal interference allocation method is proposed to minimize OP of the primary network. For the secondary network, we derive exact expressions of end‐to‐end OP and IP which are verified by Monte Carlo simulations. 相似文献
14.
Tai-Ann Chen Fitz M.P. Wen-Yi Kuo Zoltowski M.D. Grimm J.H. 《Selected Areas in Communications, IEEE Journal on》2000,18(7):1175-1190
This paper extends the traditional Clarke/Jakes (1968, 1974) model for a frequency flat fading process in a land mobile radio system to facilitate the examination of coherent space-time demodulation systems. The work develops a space-time correlation function using a ring of scatterers model around the mobile unit. The resulting correlation function permits the investigation of a variety of issues concerning base station configurations in space-time systems. The interrelationship of the fading process between the space and the time domain is explored. A detailed example regarding the effects of antenna separation in a receiver diversity system is considered. A set of design rules for interleaving depth and antenna separation in a space-time modem is presented and quantified 相似文献
15.
Combined spatial and time-frequency signatures of signal arrivals at a multisensor array are used for nonstationary interference suppression in direct-sequence spread-spectrum (DS/SS) communications. With random PN spreading code and deterministic nonstationary interferers, the use of antenna arrays offers increased DS/SS signal dimensionality relative to the interferers. Interference mitigation through a spatio-temporal subspace projection technique leads to reduced DS/SS signal distortion and improved performance over the case of a single antenna receiver. The angular separation between the interference and desired signals is shown to play a fundamental role in trading off the contribution of the spatial and time-frequency signatures to the interference mitigation process. The expressions of the receiver signal-to-interference-noise ratio (SINR) implementing subspace projections are derived, and numerical results are provided 相似文献
16.
《Vehicular Technology, IEEE Transactions on》1983,32(2):201-205
Historically, it has been difficult to combine transmitters which are closely spaced in frequency onto the same omnidirectional antenna. Two principal techniques have been used: cavity combining and transmission line hybrid combining. When using cavities, the minimum separation is limited by the amount of insertion loss that is acceptable and by the frequency stability of the cavities. In the 800- MHz land mobile frequency band, cavity combining has been used to combine transmitters as closely spaced as 0.5 MHz with 3 dB of insertion loss. When combining transmitters separated less than 0.5 MHz, hybrid combining has been used. When two transmitters are combined using this technique, half of the power of each is dissipated into a matched load. Further, each time the number of transmitters being combined is doubled, an additional 3 dB is added to the insertion loss. A new technique has been developed which utilizes transmission line hybrids to combine the transmitters, but which does not suffer from large insertion loss. The power that was previously dissipated in the resistive load is radiated in a manner that produces an omnidirectional pattern. The antenna and network that accomplish this combine signals with 90° phase shifts. Measurements show that it is possible to combine eight transmitters arbitrarily close in frequency with 35 dB of isolation between adjacent channels, less than 0.5 dB insertion loss, and with horizontal pattern circularity better than ±3 dB. Additionally, this technique can be combined with cavity combining to maintain high isolation between additional tranmitters. 相似文献
17.
Chang J.-H. Tassiulas L. Rashid-Farrokhi F. 《Wireless Communications, IEEE Transactions on》2002,1(1):16-27
The beamforming problem is studied in wireless networks where both the transmitters and receivers have linear adaptive antenna arrays. Algorithms are proposed that find the antenna array weight vectors at both the transmitters and receivers as well as the transmitter powers with one of the following two objectives: (1) to maximize the minimum signal-to-interference-and-noise ratio (SINR) over all receivers and (2) to minimize the sum of the total transmitted power satisfying the SINR requirements at all links. A numerical study is performed to compare the network capacity and the power consumption among systems having a different number of antenna array elements in a code division multiple access network 相似文献
18.
《Antennas and Propagation, IEEE Transactions on》2006,54(10):2869-2877
VHF signal strength data from two NOAA weather radio transmitters, located in southern California and southwestern Arizona, were collected over a wide range of topography ranging from relatively flat to mountainous terrain. Signal strength data were collected using a mobile receiver traveling from 20 km to over 100 km, with the receiving antenna at a constant height of 2.2 meters above the ground. Meteorological information was obtained from local radiosonde measurement stations at Miramar (NKX) and Yuma Proving Ground (1Y7). This data is used as the basis for a validation study of the Advanced Propagation Model (APM) to determine its applicability for low altitude mobile radio communications applications over terrain. 相似文献
19.
Counts T. Gurbuz A.C. Scott W.R. McClellan J.H. Kangwook Kim 《Geoscience and Remote Sensing, IEEE Transactions on》2007,45(8):2544-2553
A multistatic ground-penetrating radar (GPR) system has been developed and used to measure the response of a number of targets to produce data for the investigation of multistatic inversion algorithms. The system consists of a linear array of resistive-vee antennas, microwave switches, a vector network analyzer, and a 3-D positioner, all under computer control. The array has two transmitters and four receivers which provide eight bistatic spacings from 12 to 96 cm in 12-cm increments. Buried targets are scanned with and without surface clutter, which is a layer of rocks whose spacing is empirically chosen to maximize the clutter effect. The measured responses are calibrated so that the direct coupling in the system is removed, and the signal reference point is located at the antenna drive point. Images are formed using a frequency-domain beamforming algorithm that compensates for the phase response of the antennas. Images of targets in air validate the system calibration and the imaging algorithm. Bistatic and multistatic images for the buried targets are very good, and they show the effectiveness of the system and processing. 相似文献