Using the CSMA scheme with no hidden terminals, successful transmission of a data packet until (maximum propagation delay) after the beginning of transmission makes any other terminals recognize that someone is occupying the transmission channel. After this recognition, packets never collide. But when hidden terminals exist, some terminals, cannot recognize the use of the message channel. In the worst case, collision of packets will waste up to 2T (T is the packet length). This degrades the performance of CSMA. We propose two new media access schemes to resolve this problem. ChannelToneMultipleAccess allows each terminal to avoid collisions of its data packets to some degree by sensing the channel-tone, and extends collision detection by having the central station jam signal when collisions occur.
All the nodes sensing the BTt signal will determine that they cannot receive data. All other nodes will defer from transmitting on sensing BTr signal. This mechanism creates the hidden terminals to back-off and exposed terminals to use the channel. The trans- mitter produces the transmits the busy tone BTt and is done to protect the RTS packets. Another busy tone BTr, is put up by the receiver, acknowledges the RTS packet and provides uninterrupted protection for the incoming data packets. The RTS packet, and the receive busy tone make the chance of successful RTS reception. The DBTMA pro- tocol is the fundamental on the packet and twice narrow-bandwidth, out-of band busy tones are implemented with enough spectral separation on the unicast shared channel. BTt (the transmit busy tone) and BTr (the receive busy tone), shown whether the node is forwarding RTS packets or receiving packet transfer data, respectively. The transmits the busy tone (BTt) provides security for the RTS packets to increase the chance of successful RTS reception at the designated receiver. All nodes sensing any busy tone are not admitted to send RTS requests. When the start of the better signal is felt, a node forward and transfers the RTS packet is required to abort such transmission imme- diately (8).
The MIP 5000 Console Gateway provides access to multiple radio types using local control, tone control, Motorola digital control and MOTOTRBO control. Each Gateway interfaces to one two-way radio. All MIP 5000 Console gateways have temperature operating specifications of -30 to +60 degrees Celsius for use in extreme environments.
We consider the multiple-access relay channel with N sources, one or multiple relay and M destination node .We focus on the time-division MARC with half-duplex terminals where the sources and the relay transmit in separate time slots. These assumptions simplify practical implementation, in particular with regard to synchronization. Network coding (NC) was recognized as an effective way to improve spectral efficiency in such a setting. Information-theoretic limits for the MARC with decode-and forward (DF) and compress-and-forward (CF) protocols have been established. Diversity has been an effective technique in combating channel fading. In a relay system, the source sends its information to the relays. The relays then process the received signals, and forward them to the destination. To achieve the spatial diversity and code optimization we use joint network channel coding scheme and relays in this work employ the same non binary LDPC codes at the physical layer and generate then networked coded packets based on symbol-wise combination of incoming packets with randomly generated non binary coefficients. This allows the relays to process and forward packets independently without pre-scheduled collaboration, rendering the proposed solution suitable for large-scale multi-path multi-hop wireless networks.
ABSTRACT: This paper deals with the assessment of measuring the quality of tone mapped images by considering the Tone Mapping Operators (TMOs) that convert high dynamic range (HDR) to low dynamic range (LDR) images provide practically useful tools for the visualization of HDR images on standard LDR displays. Different TMOs create different tone mapped images, and a natural question is which one has the best quality. Without an appropriate quality measure, different TMOs cannot be compared, and further improvement is directionless. Subjective rating may be a reliable evaluation method, but it is expensive and time consuming, and more importantly, is difficult to be embedded into optimization frameworks. Here we propose an objective quality assessment algorithm for tone mapped images by combining two concepts one of them is a multi scale signal fidelity measure on the basis of a modified structural similarity index and the other followed by a naturalness measure on the basis of intensity statistics of natural images. Validations using independent subject-rated image databases show good correlations between subjective ranking score and the proposed tone-mapped image quality index (TMQI). The proposed measure not only provides an overall quality score of an image, but also creates multi-scale quality maps that reflect the structural fidelity variations across scale and space.
The main goal of this research is to combine some mechanisms for minimizing network congestion in order to provide efficient communication in WSN. The mechanisms are network self-organizing with load balancing strategy, hop by hop flow control, and collisions reduction. To realize the combined mechanisms, this research designs a new WSN protocol that called Multi-Channel Time Division MultipleAccess – Cross Layer Protocol (MT-XLP). Design of this cross layer protocol integrates Medium Access Control (MAC) layer and network/routing layer. MAC layer deals with channel assignment and time slot allocation to provide communication link in the network and reduce collisions. Network/routing layer deals with mechanism for load balancing and hop by hop flow control. By means of MT-XLP, performance of the combined mechanisms in minimizing network congestion is evaluated. The performance evaluation is conducted by measuring packet throughput and index of throughput fairness. Finally, performance evaluation is benchmarked with IEEE 802.15.4/ZigBee.
Your cordless digital telephone uses advanced technology and provides important features that place it far above the competition in functionality and value. You benefit from much greater performance than other cordless telephones currently available. This means better sound quality, longer range, greater security, multi-line access, helpful LCD display information, and many other important advantages.
If your station is in Do Not Disturb (DND) mode, internal, external and transferred calls do not ring your station and Off-hook Call Announce calls are denied. You can continue to make calls while in the DND mode. When originating a call in DND mode, you will hear a short burst of interrupted dial tone followed by continuous dial tone. You can start dialing at any time during either tone.
Multicarrier Code Division MultipleAccess (MC-CDMA) is a digital modulation and multicarrier scheme which results from the combination of Orthogonal Frequency Division Multiplexing (OFDM) and Code Division MultipleAccess (CDMA). Based on this combination, three multipleaccess techniques are formed, viz: Multicarrier (MC) –CDMA, Multicarrier Direct Sequence (DS)-CDMA and Multitone (MT)-CDMA. Therefore, these multipleaccess schemes have both the advantages and disadvantages of the elements that constitutes them. Hence, these multicarriers techniques are further classified into frequency domain and time domain spreading codes. In case of frequency domain , the
The core of DVB-RCS could be a multi-frequency Time Division MultipleAccess (MF-TDMA) transmission theme for the return link, that provides high bandwidth efficiency for multiple users. The demand-assignment theme uses several capability mechanisms that enable improvement for various categories of applications, so voice, video streaming, file transfers and net browsing will all be handled with efficiency. DVB-RCS supports many access schemes creating the system far more responsive, and so additional economical than ancient demand-assigned satellite systems. This access themes area unit combined with a versatile transmission scheme that has progressive turbo writing, many burst size choices and economical informatics encapsulation choices. These tools enable systems to be fine-tuned for the most effective use of the facility and information measure satellite resources.
In the following, we will focus on the “sense-before- transmit” version of CSMA, i.e., without collision avoidance mechanisms based on preliminary handshakes. According to the terminology established by Tobagi and Kleinrock  (TK for short), in non-persistent CSMA (np-CSMA) the node backs off and reschedules a later transmission attempt whenever the channel is sensed busy.
where H is channel matrix, and w is Gaussian noise vector. In SM, each transmitter supports the same constellation symbol by activating a given number of antennas according to the input bit sequence ,. In this paper it is assumed that the users activate the same number of antennas, i.e. = × where, S is total number of antennas simultaneously active amongst the K mobile stations. The transmit signal of u-th SM transmitter can be expressed as
Abstract —In this letter, we propose a robust beamforming design for non-orthogonal multipleaccess (NOMA) based multiple-input single-output (MISO) downlink systems. In particular, the robust power minimization problem is studied with imperfect channel state information (CSI), where the beam- formers are designed by incorporating norm-bounded channel uncertainties to provide the required quality of service at each user. This robust scheme is developed based on the worst-case performance optimization framework. In terms of beamforming vectors, the original robust design is not convex and therefore, the robust beamformers cannot be obtained directly. To cir- cumvent this non-convex issue, the original intractable problem is reformulated into a convex problem, where the non-convex constraint is converted into a linear matrix inequality (LMI) by exploiting S-Procedure. Finally, simulation results are provided to demonstrate the effectiveness of the proposed robust design.
decoding aspects, hence is out of scope of this paper. In DF relaying, channel decoding is performed at the relay before NC and forwarding. On the other hand, in the DMF case, only demodulation is performed at the relay. As such, DMF has less computational complexity than DF but it is more prone to decoding errors at the relay. For each protocol, we develop two new channel-aware JNCD algorithms. To summarize, the contributions of the paper are as follows: we show that JNCD provides better perfor- mance than separate network channel decoding only if the destination has enough knowledge of the decoding error probability at the relay; in addition, this gain will be larger as the number of fading blocks per codeword increases. Also, it is shown that the number of pilot symbols mostly affects the coding gain of the system with a negligible impact on the diversity order, at least for the signal-to- noise ratio (SNR) range of interest. Finally, it is shown that CSI quantization errors affect both coding gain and diversity order. Additionally, it is shown that, in general, 3-bit quantization is sufficient for DMF relaying and 6-bit quantization is needed for DF relaying.
We study the relation between the stable throughput regions and the capacity regions for a Gaussian multiple-accesschannel. Our main focus is to study how the extent of side information about source arrival statistics and/or instantaneous queue states at each transmitter influence the achievable stable throughput region. Two notions of MAC capacity are studied. The first notion is the conventional Shannon capacity which relies on large coding block lengths for finite SNR, while the second uses finite code blocks with high SNR. We find that the stable throughput region coincides with the Shannon capacity region for many scenarios of side information, where side information is defined as a mix of statistical description and instantaneous queue states. However, a lack of suﬃcient side information about arrival statistics can lead to a significant reduction in the stable throughput region. Finally, our results lend strong support to centralized architectures implementing some form of congestion/rate control to achieve Shannon capacity, primarily to counter lack of detailed information about source statistics at the mobile nodes.
Abstract: A multiple-input multiple-output (MIMO) communication system combined with the orthogonal frequency division multiplexing (OFDM) modulation technique can achieve reliable high data rate transmission over broadband wireless channels. Channel state information for both single- input single-output (SISO) and MIMO systems based on pilot aided arrangement is investigated in this paper. The estimation of channel at pilot frequencies with conventional Least Square (LS) and Minimum Mean Square (MMSE) estimation algorithms is carried out through Matlab simulation. The performance of MIMO OFDM and SISO OFDM are evaluated on the basis of Bit Error Rate (BER) and Mean Square Error (MSE) level. Further enhancement of performance can be achieved through maximum diversity Space Time Block Coding (STBC) and Maximum Likelihood Detection at transmission and reception ends respectively. MMSE estimation has been shown to perform much better than LS but is more complex than LS for the MIMO system using pilot carriers.
The system model in this work is a typical multipleaccess wiretap channel (MAC-WT) 1 , which has been intensively studied recently. However, all of these refer- ences [21–34] considered problems from an information- theoretical perspective and characterized the setting as a whole. Ender Tekin et al. characterized secrecy rate regions and an upper bound for the secrecy sum-rate for a Gaussian MAC-WT via the Gaussian encoding in . They also addressed a fading MAC-WT in , providing achievable ergodic secrecy rate regions as well as its outer bounds and giving optimal power allocations to maximize the sum-rate. Hassan Zivari-Fard et al.  investigated a 2-user MAC-WT with a common message which can be decoded by both the legitimate receiver and the eaves- dropper, and derived general inner and outer bounds on a secrecy capacity region for both discrete memoryless and Gaussian cases. The authors further addressed this type of MAC-WT (with a common message) in , where only one transmitter’s private messages should be kept secret from the adversary. They derived general inner and outer bounds for both imperfect and perfect secrecy conditions for the adversary under discrete memory- less, less noisy, and Gaussian versions of the MAC-WT. Yet, the secure degrees of freedom (DoF) of such Gaus- sian signaling-based schemes are zero, which means the schemes are suboptimal and leads to further work for new encoding techniques. One commonly used encod- ing technique is the real interference alignment [25–27]. Other techniques, e.g., uniform distributed source coding