csma ca carrier sense multiple access with collision avoidance

... (Code Division Multiple Access) .13 2.2. 2CSMA/ CD (Carrier Sense Multiple Access with Collision Detection): .13 2.2. 3CSMA/ CA (Carrier Sense Multiple Access with Collision Avoidance) ... thu ngưng tranh chấp kênh đợi đến node khác truyền truyền xong 2.2.3 CSMA/ CA (Carrier Sense Multiple Access with Collision Avoidance) Đa truy xuất cảm nhận sóng mang với tránh đụng độ Thay khởi ... lượng lớn hơn, khiến máy thu hoạt động truyền đến từ nút cần dự tính 2.2.2 CSMA/ CD (Carrier Sense Multiple Access with Collision Detection): Đa truy xuất cảm nhận sóng mang với thăm dò đụng độ...

Ngày tải lên: 28/03/2014, 13:20

... LTE Nhóm The subcarriers used for physical layer processing purposes are the ones that carry reference The subcarriers used for physical layer processing purposes are the ones that carry reference ... subcarrier in the synchronization sequence (PSS) allowed bandwidth - Unlike the preamble in WiMAX, the number of subcarriers used for PSS - The pseudorandom sequence to be sent on the subcarriers ... subcarriers are grouped as a unit in the subcarriers in an OFDM symbol frequency axis, and OFDM symbols (or OFDM symbols in A slot is formed by combining a subchannel with different special cases)...

Ngày tải lên: 24/07/2015, 22:26

... toàn cầu) IS-95,tương ứng với điều hỗ trợ cho liệu tốc độ cao [3] Phương pháp cần đầu tư nhiều công nghệ vô tuyến mạng lõi dẫn đến chi phí cao.trong mạng không dây 4G,dự kiến đài phát tích hợp phục ... vào tính hiệu lượng [2] Trong WiMAX, phương pháp phân kênh bắt buộc gọi PUSC ( Partially Used SubCarrier ), kênh hình thành cách nhóm 24 sóng mang trình bày phần khác quang phổ Lựa chọn giả ngẫu ... ra(MIMO-OFDM) công nghệ yếu tố quan trọngtrong việc lựa chọn OFDMA [1, 2] công nghệ MIMO giúp đạt hiệu phổ cao MIMO-OFDM, chứng minh thành công IEEE 802.11n Một số nhược điểm tỷ số công suất đỉnh công suất...

Ngày tải lên: 24/07/2015, 22:27

... shift keying (QPSK) Sophisticated multiple access technology like frequency division multiple access (FDMA), time division multiple access (TDMA) and code division multiple access (CDMA) also gained ... chosen while single carrier frequency division multiple access (SC-FDMA), which uses similar wireless air interface as OFDMA, is the chosen uplink multiple access technology [8] Multiple antennas ... Interference Cancellation 81 4.3.1 4.3.2 Successive Interference Cancellation 83 4.3.3 Multiple Access Interference in Different SIC Stages 86 4.3.4 4.4 Multiple Access Interference...

Ngày tải lên: 08/09/2015, 18:24

... Hybrid allocation Subcarriers … … … Time Interleaved allocation (c) OFDM-FDMA with different subcarrier allocation schemes Fig.1.4: Typical multiple access techniques used with OFDM A number of ... Subcarriers … … Time Slot Frame (a) OFDM-TDMA Subcarriers Time …… user U user user Code (b) OFDM-CDMA Subcarriers Subcarriers … user U … … user … user Time Time Block allocation Hybrid allocation ... of multiple access schemes to share resources among different users Typical OFDM-based multiple access techniques include Time Division Multiple Access (OFDM-TDMA), Code Division Multiple Access...

Ngày tải lên: 14/09/2015, 14:03

... depicted cases with multiple users, that is, there is virtually no loss in power efficiency compared to the case without MAI We therefore obtain a quasiorthogonal multiple access without the need ... window length, which is Kc − L in the case of block fading With (7) and (10), we can get a lower bound for the MSE with tb-LS as The mean-squared error (MSE) can be calculated as vtb - LS = E U · (L ... consideration An alternative interpretation are transmissions with a significantly higher carrier frequency and/or shorter chip duration If we increase the carrier frequency to fC = 50 GHz and decrease the...

Ngày tải lên: 22/06/2014, 23:20

... extended to cases with multiple users The outage capacity issue for single-user multiple- input multiple- output (MIMO) case was studied extensively In [1], the authors characterized the outage capacity ... proposed in [12] to maximize the sum capacity of a time invariant Gaussian MIMO multiple- access channel The ergodic capacity region for MIMO multiple- access channel with covariance feedback has been ... system capacity The fundamental question addressed is the ultimate capacity achievable with a MAE array equipped base station communicating with multiple mobile stations Since there are multiple...

Ngày tải lên: 23/06/2014, 01:20

... attempting to determine if the channel is in use Carrier sense multiple access (CSMA) and carrier sense multiple access/ collision avoidance (CSMA/ CA) are both contention-based Random wait Random ... practice 1.2.2 Carrier Sense Multiple Access and Carrier Sense Multiple Access/ Collision Avoidance The main drawback to ALOHA and Slotted ALOHA is that transmitters blindly transmit without attempting ... Access Control 15 1.2.1 ALOHA .16 1.2.2 Carrier Sense Multiple Access and Carrier Sense Multiple Access/ Collision...

Ngày tải lên: 27/06/2014, 14:20

Ngày tải lên: 25/07/2014, 09:39

... Access Control 15 1.2.1 ALOHA .16 1.2.2 Carrier Sense Multiple Access and Carrier Sense Multiple Access/ Collision ... understood orthogonal access techniques such as time division multiple access and frequency division multiple access Additionally, random access schemes such as carrier sense multiple access are examined ... 28, 2006 15:54 CODE DIVISION MULTIPLE ACCESS (CDMA) Multiple access techniques Conflict-free Contention-based Random access Collision resolution ALOHA, CSMA, CSMA/ CA, RTS/CTS, etc TREE, WINDOW,...

Ngày tải lên: 07/08/2014, 21:20

... attempting to determine if the channel is in use Carrier sense multiple access (CSMA) and carrier sense multiple access/ collision avoidance (CSMA/ CA) are both contention-based Random wait Random ... practice 1.2.2 Carrier Sense Multiple Access and Carrier Sense Multiple Access/ Collision Avoidance The main drawback to ALOHA and Slotted ALOHA is that transmitters blindly transmit without attempting ... significant overhead in the already crowded spectrum allocated for WLANs The 802.11 MAC layer [18] is based on the CSMA/ CA + ACK protocol for unicast frames and the CSMA/ CD (carrier sense multiple access/ collision...

Ngày tải lên: 07/08/2014, 21:20

... MULTIPLE ACCESS (CDMA) FIGURE 2.4: Comparison of original/despread signal and spread signal spectra for DS/SS with square pulses 2.2.2 Multiple Access The DS/SS technique can be expanded to multiple ... TECHNIQUES FOR CODE DIVISION MULTIPLE ACCESS 45 structure described is optimal only in the absence of multiple access interference Time hopping can be thought of as DS/SS with tertiary (three-valued) ... bandwidth expansion is through frequency hopping In FH/SS, the carrier frequency of the data modulated sinusoidal carrier is periodically changed over some predetermined bandwidth By “hopping”...

Ngày tải lên: 07/08/2014, 21:20

... a receiver with a single correlator sees a degradation in performance since it captures only a portion of the energy However, a receiver with multiple correlators (Rake fingers) can capture all ... two-path case It can be seen that, even with a relatively weak second path, decent diversity gains are provided Thus, a P2: IML MOBK023-Buehrer.cls September 28, 2006 15:54 CODE DIVISION MULTIPLE ACCESS ... requirement for additional channel estimation, which can be substantial 2.6 MULTIPLE ACCESS PERFORMANCE OF DIRECT SEQUENCE CODE DIVISION MULTIPLE ACCESS The previous section examined the performance...

Ngày tải lên: 07/08/2014, 21:20

... 2006 15:55 CODE DIVISION MULTIPLE ACCESS (CDMA) 3.1.4 Statistical Multiplexing The final fundamental CDMA concept that we will discuss in this section is termed statistical multiplexing, which is ... statistics with and without voice activity (K = 25, N = 64, υ = 0.5) P1: IML/FFX MOBK023-03 P2: IML MOBK023-Buehrer.cls September 28, 2006 15:55 CELLULAR CODE DIVISION MULTIPLE ACCESS 83 with and without ... typical CDMA systems, a mobile can, in many situations, communicate with three base stations simultaneously, resulting in three-way soft hand-off This provides further improvement, although, as with...

Ngày tải lên: 07/08/2014, 21:20

... Obviously, uplink capacity is most useful when paired with similar downlink capacity Thus, we wish to find the capacity of the downlink as well Whereas uplink capacity is primarily concerned with interference ... ourselves with only the capacity of a CDMA system However, because the system is interference-limited, a fundamental relationship—specifically, an inverse relationship—exists between the system capacity ... performance is identical P1: IML/FFX MOBK023-03 P2: IML MOBK023-Buehrer.cls 96 September 28, 2006 15:55 CODE DIVISION MULTIPLE ACCESS (CDMA) to the single-sector case However, we can reduce the total...

Ngày tải lên: 07/08/2014, 21:20

... are termed the multiple access collision avoidance/ common-transmitter (MACA/C-T) and the multiple access collision avoidance/ receiver-transmitter (MACA/R-T) protocols [46] CSMA can also be added ... 802.11 standard for WLANs In such a scheme, codes can be assigned dynamically for multiple access based on the communication needs of the node The codes can be chosen from a set of pre-defined codes, ... compared to the CSMA and the RTS/CTS mechanism with a single spreading code because multiple sessions can occur simultaneously as adjacent nodes transmitting would ideally avoid interfering with each...

Ngày tải lên: 07/08/2014, 21:20

... the limiting factor in the capacity of CDMA systems As a result, capacities for single-cell CDMA systems can be substantially lower than those for orthogonal multiple access techniques such as ... receivers that can approach the performance of the optimal receiver with significantly reduced computational complexity These sub-optimal receivers can be broken down into two general categories, ... channel is potentially more harsh but can support a more sophisticated receiver User signals arrive at the base station receiver asynchronously and can have significantly different energies, resulting...

Ngày tải lên: 07/08/2014, 21:20

... users With two stages of full cancellation, approximately 45 users can be supported However, by applying partial cancellation with a partial cancellation factor of 0.6 in the first stage of cancellation ... feedback Another case where the performance converges as the number of stages increases is the linear cancellation case which can be thought of as partial cancellation with the partial cancellation ... Interference Cancellation (non-linear, wideband cancellation implementation) As in SIC detectors, PIC can be implemented in linear form Specifically, we can directly use the matched filter outputs without...

Ngày tải lên: 07/08/2014, 21:20

... radio channels: Part II—The hidden terminal problem in carrier sense multiple- access and the busy-tone solution,” IEEE Transactions on Communications, vol 23, pp 1417–1433, December 1975 doi:10.1109/TCOM.1975.1092767 ... Data Communications, pp 39–49, 1997 [17] Z J Haas and J Deng, “Dual busy tone multiple access (DBTMA)—a multiple access control scheme for ad hoc networks,” IEEE Transactions on Communications, ... nine stages of interference cancellation can increase cell capacity nearly times A single stage of cancellation gets nearly half of that improvement while four stages of cancellation obtain nearly...

Ngày tải lên: 07/08/2014, 21:20

... Channel – kênh điều khiển dùng chung tốc độ cao), HS-DPCCH (High Speed Dedicated Physical Control Channel – kênh điều khiển vật lý dành riêng tốc độ cao) HS-PDSCH (High Speed Downlink Shared Channel ... thiện hiệu suất HSPA VoIP ứng dụng tương tự khác Hiệu suất trải phổ cao dung lượng tế bào cao yêu cầu để đáp ứng tốc độ bít cao vài thiết bị với vị trí trạm gốc Hình 1.10 minh họa cho dung lượng ... vùng Caribbe (16).HSDPA nhiều vùng có tốc độ download lên tới 7,2 MB/giây, bình thường đạt từ 800 KB/giây đến MB/giây Tuy nhiên, tốc độ mạng không Có tới 62% số mạng có tốc độ download cao 3,6...

Ngày tải lên: 02/06/2015, 17:26