cài đặt giao thức cửa sổ trượt kích thước 1 bit a one bit s
Code Division Multiple Access (CDMA) phần 1 doc
Ngày tải lên :
07/08/2014, 21:20
... division multiple access Additionally, random access schemes such as carrier sense multiple access are examined In Chapter 2, basic spread spectrum techniques that are used in CDMA systems are reviewed, ... per symbol and α is a constant related to the filtering, pulse shape, and modulation scheme There are advantages and disadvantages of TDMA as compared to other multiple access schemes One advantage ... channels, that must also be shared A logical channel can be defined as some fraction of the available access medium that is used by a particular transmit/receive pair The system may contain only a single...
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Code Division Multiple Access (CDMA) phần 2 doc
Ngày tải lên :
07/08/2014, 21:20
... CDMA and SSMA in that CDMA specifically designs its spreading waveforms to have low cross-correlation properties, whereas SSMA systems have independent codes that may also have low cross-correlation ... broadcast frames It also deploys a virtual carrier sense mechanism (using RTS/CTS) to avoid a station from transmitting when two nodes are already communicating 1. 3 MULTIPLE ACCESS WITH SPREAD SPECTRUM ... node has begun transmission of the CTS packet and, at the same time, an RTS packet is sent, the node transmitting the RTS packet hears the CTS packet and refrains from accessing the channel Haas...
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Code Division Multiple Access (CDMA) phần 3 potx
Ngày tải lên :
07/08/2014, 21:20
... impossible in a decentralized system 2.4 TIME HOPPING As a final example of CDMA, consider a pulse-based system where transmissions are based on a series of low duty cycle pulses as in impulse-radio ... Walsh codes are good candidates for spreading codes only for synchronous systems; they are clearly poor candidates for asynchronous systems However, there are several families of codes that have good ... codes is higher by at least a factor of √ than that of optimal codes Another set of codes called Kasami sequences [1, 25, 26] can be constructed from m-sequences These sequences have a cardinality...
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Code Division Multiple Access (CDMA) phần 4 pdf
Ngày tải lên :
07/08/2014, 21:20
... system by modeling the decision statistic used for symbol estimation as a Gaussian random variable This means we must assume that MAI after despreading is well modeled as a Gaussian random variable ... MOBK023-Buehrer.cls September 28, 2006 15 :54 SPREAD SPECTRUM TECHNIQUES FOR CODE DIVISION MULTIPLE ACCESS 59 b1,0 User a1 ,0 a1 ,1 a1 ,2 a1 ,3 a1 ,4 a1 ,N -1 Δk ζkTc τk User k ak,0 a1 ,5 ak,N-3 ak,N-2 ak,N -1 ak,0 ak ,1 ... is actually less severe In other words, while we assumed in the last section that each Rake finger was subject to Rayleigh fading, this is usually found to be a pessimistic assumption, especially...
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Code Division Multiple Access (CDMA) phần 5 ppt
Ngày tải lên :
07/08/2014, 21:20
... impact of multiple simultaneous transmissions also known as MAI We showed that in fading environments, spread spectrum signals provide a substantial performance advantage over narrowband signals ... multiple access techniques, let us first pursue a firstorder comparison of the capacity of FDMA, TDMA, and CDMA based on average SINR performance Let us assume that a system has a total bandwidth ... particularly cellular systems Propagation losses allow frequency bands to be reused in geographically separated locations This increases the overall capacity of wireless systems However, in a given area,...
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Code Division Multiple Access (CDMA) phần 6 docx
Ngày tải lên :
07/08/2014, 21:20
... all users use the system simultaneously but randomly access the system This effect was discussed in Chapter and impacts all types of cellular systems regardless of the multiple access technique ... single sector (K = 10 ) 10 Load = Erlangs Load = Erlangs Load = Erlangs Load = Erlangs -1 Probability of blocking 10 -2 10 -3 10 -4 10 -5 10 10 11 12 13 14 15 16 17 18 19 Number of CEs FIGURE 3 .13 : ... dedicated hardware must be available for demodulation, decoding, framing, and so on Since dedicated hardware has an associated cost, minimizing the necessary hardware at the base station is a priority...
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Code Division Multiple Access (CDMA) phần 7 pps
Ngày tải lên :
07/08/2014, 21:20
... assigned on a call-by-call basis, so a channel access strategy is required as was discussed in the previous section The channel access techniques are analogous to the random access methods described ... centralized voice-centric systems described in Chapters 1 3, codes are assigned on a callby-call basis, which is a classic CDMA approach In packet radio systems, separate codes are not typically assigned ... random access protocols, channel access strategies for SS/PRNs allow for multiple simultaneous transmissions in the same geographic area The most common channel access technique used for SS/PRNs is...
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Code Division Multiple Access (CDMA) phần 8 potx
Ngày tải lên :
07/08/2014, 21:20
... have assumed that all values of Ak are equal If they are not equal, the transformation matrix is still (approcimately) diagonal and thus the transformation simply applies a constant scaling factor ... MAI tends toward a Gaussian distribution (see Chapter for details) However, we have also seen that this MAI is the limiting factor in the capacity of CDMA systems As a result, capacities for single-cell ... synchronous, zero phase synchronous, random phase asynchronous, zero phase asynchronous, random phase (5 .10 ) Now, assuming synchronous reception of signals with equal (zero) phase ( = 1) and equal received...
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Code Division Multiple Access (CDMA) phần 9 docx
Ngày tải lên :
07/08/2014, 21:20
... that increases with the cancellation stage This reflects the fact that estimates in the early stages are less reliable than estimates in the later stages and mitigates the negative impact of canceling ... conventional first stage as compared to a two-stage receiver with a decorrelating first stage Assuming a conventional matched filter first stage, the bit estimate for signal at the output of the second stage ... Mathematically, we can represent the bit decisions for an S- stage parallel cancellation scheme at any stage s as (s ˆ (s b k ) = sgn zk ) (5.69) (s where zk ) is the decision metric after s stages...
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Code Division Multiple Access (CDMA) phần 10 pot
Ngày tải lên :
07/08/2014, 21:20
... spreading sequence of the kth user representing both the long and sort codes, ni (t) is complex Gaussian noise that has variance σn in in-phase and quadrature and is assumed to be spatially and ... Control, and Coding As discussed in Chapter 3, one of the advantages of CDMA systems, and IS-95 in particular, is that voice activity is exploited to enhance capacity During a typical conversation, a ... is modeled by assuming a sufficiently high thermal noise level so as to include its effect This is inadequate for a couple of reasons First, as system loading increases, the OCI should increase...
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Code Division Multiple Access CDMA pdf
Ngày tải lên :
27/06/2014, 14:20
... systems 2 .1 FORMS OF CODE DIVISION MULTIPLE ACCESS CDMA is also known as spread spectrum multiple access or SSMA because the use of spread spectrum waveforms is fundamental to CDMA .1 Spread spectrum ... down-conversion, the signal is despread and passed to a standard BPSK detector This process can be envisioned in two ways First, we can view the spreading/despreading operations as transparent additions ... waveforms (in additive white Gaussian noise channels and fading channels) as well as the multiple access performance are examined Special emphasis is given to fading channels since spread spectrum is...
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BÀI BÁO CÁO -Công nghệ WCDMA(wideband code division multiple access) và tình trạng triển khai
Ngày tải lên :
02/06/2015, 17:26
... Hình 1. 10 minh h a cho dung lượng tế bào dự tính sector 5MHz với WCDMA, với HSPA s với HSPA cải tiến môi trường vĩ mô tế bào.HSPA s bao gồm có anten nhận Rake thiết bị đầu cuối an ten nhánh a ... HSDPA phát triển d a công nghệ W-CDMA, s dụng phương pháp chuyển đổi mã h a liệu khác Nó tạo kênh truyền liệu bên W-CDMA gọi HS-DSCH (High Speed Downlink Shared Channel), hay gọi kênh chia s ... Kiến trúc giao thức phẳng người s dụng HSDPA HSUPA Chức s lớp giao thức khác có hiệu lực với HSDPA HSUPA giống với Re’99 Kiến trúc xác định phần phẳng người s dụng thực liệu người s dụng điều...
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theory of code division muitiple access communication
Ngày tải lên :
01/06/2014, 11:27
... mentioned above, in an ultrawideband system, such as impulse radio, fading is not nearly as serious a problem as it is for narrowband systems Impulse radio systems can operate at variable bit rates ... important advantage in comparison with DS CDMA systems In the DS CDMA system, the signals have a large instantaneous bandwidth The complexity and cost of the transmitter increases as the instantaneous ... (1. 17) for the radio channel capacity is valid also for forward link The forward link transmission that is one- to-many transmission has some advantages in comparison to many-to -one transmission...
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Báo cáo hóa học: " Iterative Pilot-Layer Aided Channel Estimation with Emphasis on Interleave-Division Multiple Access Systems Hendrik Schoeneich and Peter Adam Hoeher" docx
Ngày tải lên :
22/06/2014, 23:20
... this paper, it is shown that this is also possible in the case of channel estimation The proposed channel estimation scheme makes use of a superimposed pilot layer (PLACE) Linear LS and MMSE as ... training sequence based channel estimation,” in 1st IEEE Signal Processing Workshop on Signal Processing Advances in Wireless Communications (SPAWC ’97), pp 12 9 13 2, Paris, France, April 19 97 E De Carvalho ... the MSE of the bias-free channel estimates This result is especially interesting in the context of IDMA, where the superimposed data layers can be well approximated as a Gaussian random variable...
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Báo cáo hóa học: " Bounds on the Outage-Constrained Capacity Region of Space-Division Multiple-Access Radio Systems" docx
Ngày tải lên :
23/06/2014, 01:20
... 20-year career at AT&T Bell Labs, most of which was spent in basic research as EURASIP Journal on Applied Signal Processing a contributing researcher and research manager At Columbia, he was involved ... use of multiple antennas at the base station can greatly increase the allowable transmission rates from the mobiles For example, with and 16 antenna elements and joint decoding at the base station, ... 10 % and 1% outage capacity regions with 2, 4, 8, and 16 antenna elements at the base station With antenna elements at the base station, both mobiles can simultaneously transmit at 0.72 nat per second...
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Thuyết trình Orthogonal Frequency Division Multiple Access in WiMAX and LTE A Comparison
Ngày tải lên :
24/07/2015, 22:26
... subcarriers used for physical layer processing purposes are the ones that carry reference symbols, plus primary and secondary synchronization sequences symbols, plus primary and secondary synchronization ... in a band user feeds back the best bands - Based on this, BS chooses bins in one of these bands and allocates the same bin over three consecutive OFDM symbols - Frequency diversity and MUD-based ... signal (PSS) and secondary synchronization signal Nhóm (SSS) PERFORMANCE BOUNDS FOR SYNCHRONIZATION AND CHANNEL ESTIMATION WiMAX PUSC mode: Maximum delay spread Nhóm Maximum Doppler spread Maximum...
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Tiểu luận Orthogonal Frequency Division Multiple Access in WiMAX and LTE A Comparison
Ngày tải lên :
24/07/2015, 22:27
... thông phổ biến cho WiMax 10 MHz, có ý ngh a có 10 24 s ng mang 1/ 3 ( bảo vệ s ng mang con) s dụng cho truyền dẫn preamble Performance Bounds For Syschronization and Channel Estimation Thông thường, ... lý kích thước cố định (PRUs) từ s ng mang con, sau s dụng để hình thành DRUs LRUs (distributed and contiguous localized resource units) Với băng thông cho trước, việc l a chọn s lượng DRUs LRUs ... ứng Doppler spread lớn 10 kHz Doppler spread cao so nhiều so với khả xảy thực tế hầu hết hệ thống WiMax triển khai Trong LTE, ước lượng kênh không hoàn toàn thực s dụng tín hiệu PSS SSS Do đó, ước...
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