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- How to make the best of 802.11 multipath environments
- In a post titled Wi-Fi 101: Multipath environments and how they affect Wi-Fi propagation, I examined what happens to 802.11 RF signals when they encounter physical obstacles. I would like to take the next logical step and develop quantifiable relationships between three different Line of Sight LoS environments and the...
- Tags: IEEE 802.11, Environment, Technology, Antenna, RF, Free Space Path Loss, Multipath Interference, Diversity Scheme, Receiver, Wireless LANs, Wi-Fi, Wireless, Michael Kassner
- Blog posts 2007-10-30
Additional Resources
- On Cyclic Delay Diversity in OFDM Based Transmission Schemes
- Cyclic Delay Diversity CDD is a simple approach to introduce spatial diversity to an Orthogonal Frequency Division Multiplexing OFDM based transmission scheme that itself has no built-in diversity. It also can be regarded as a Space-Time Code STC. But in contrast to that there is no additional effort in the...
- Tags: Diversity, Cyclic Delay Diversity, OFDM, Wireless
- White papers
- A Simulation Study of Packet Path Diversity for TCP File Transfer and Media Transport on the Internet
- This paper studies the performance of TCP-based media transport when combined with Packet Path Diversity PPD in the Internet. A simple PPD-TCP transport scheme is presented where the ACKnowledgments ACKs from the receiver are duplicated and sent across independent network paths. It also investigates a PPD-TCP scheme where in addition...
- Tags: Network, Stanford University, Media, TCP, Path, Tcp/Ip, Internet, Networking
- White papers 2007-01-01
- On Performance of Multiuser OFDM Systems With Transmit Diversity
- Performance of multiuser orthogonal frequency division multiplexing OFDM systems with transmit diversity over the frequency selective fading channel is explored in this paper. A signal model for the multiuser OFDM system is developed using Alamouti's transmit diversity scheme and the minimum mean square error MMSE method is applied to detect...
- Tags: Performance, OFDM, Wireless
- White papers 2004-11-30
- How to achieve real diversity in IT
- While just hiring people who look different may satisfy internal mandates or passing fads, the truly beneficial form of diversity comes from a diversity of ideas and experience. by Patrick Gray
- Tags: Hiring, Information Technology, Diversity, Patrick Gray, Prevoyance Group, Strategy, Management
- Blog posts 2008-09-03
- Techniques for Bluetooth Performance Improvement
- This paper examines the application of some techniques in Bluetooth communications expected to improve system's performance under certain environmental conditions. The transmitter diversity Alamouti scheme and receiver diversity have been evaluated and compared to the standard single antenna transmitter and receiver system by means of the achievable BER. Some analytical...
- Tags: Technique, Transmitter, Bluetooth, Productivity, Wireless
- White papers
- Temporal Diversity Assisted Blind Channel Estimation for Downlink Long-Code CDMA Systems
- In CDMA downlink, subspace channel estimation can not be applied directly since long spreading codes destroy the rank condition of the received data covariance matrix. However, after introducing temporal diversity in the transmitted chip sequence for all users, subspace technique can be applied to estimate channel. Detection of the desired...
- Tags: University Of California, Channel Estimation, Productivity, Performance Management, Cellular Phones, Human Resources, Workforce Management, Consumer Electronics, Personal Technology
- White papers
- A Reduced Complexity Channel Estimation for OFDM Systems With Precoding and Transmit Diversity in Mobile Wireless Channels
- A precoding approach for reduced complexity channel estimation for OFDM systems with transmit diversity is presented. Two different OFDM schemes that employ the precoding are investigated: the first one is based on space-time coding, the second is based on a transmit diversity using an optimal design of symbols for channel...
- Tags: Mobile, Diversity, Channel Estimation, OFDM, Wireless
- White papers 2006-02-07
- An Opportunistic Downlink MIMO-OFDM Scheme
- This paper presents an opportunistic Multiple-Input Multiple-Output MIMO scheme that achieves increased throughput of multi-user downlink transmission in frequency-selective channels. Developed for OFDM systems, the main idea of the proposed scheme is to find the optimal subset of users for each subchannel and optimal transmit beamforming vector which would maximize...
- Tags: Radio, Scheme, OFDM, Advertising & Promotion, Wireless, Marketing
- White papers 2006-01-17
- Differential Modulation Diversity for OFDM
- The application of Differential Modulation Diversity DMD to orthogonal frequency division multiplexing with multiple transmit and/or receive antennas is considered. Based on diagonal signals originally designed for differential space-time modulation, DMD is used to exploit both space and frequency diversity. At the receiver, low-complexity decision-feedback differential detection without channel state...
- Tags: University Of Toronto, OFDM, Wireless
- White papers
- Maximum Achievable Diversity for MIMO-OFDM Systems With Arbitrary Spatial Correlation
- In this paper, the maximum achievable diversity order is determined for MIMO-OFDM systems with arbitrary spatial correlation. This paper shows that the maximum achievable diversity order is the rank of the spatial correlation matrix of the channel including all delay paths. The paper also shows that any space-frequency code designed...
- Tags: Diversity, MIMO-OFDM
- White papers 2004-08-23
- Source Selectable Path Diversity Via Routing Deflections
- This paper presents the design of a routing system in which end-systems set tags to select non-shortest path routes as an alternative to explicit source routes. Routers collectively generate these routes by using tags as hints to independently deflect packets to neighbors that lie off the shortest-path. It show how...
- Tags: Association For Computing Machinery, Internet Service Providers (ISPs), Internet, Routers & Switches, Networking, Network Technology
- White papers 2006-09-15
- Cooperative Diversity in Wireless Networks: A Geometry-Inclusive Analysis
- Cooperation between physically separated wireless nodes can achieve the high Signal-to-Noise Ratio SNR diversity gains characteristic of multi-antenna arrays. Simulations indicate that such gains are still achieved for SNRs in the range of practical interest for several applications. Cooperation further yields SNR gains in addition to diversity gains. In contrast...
- Tags: Network, Gain, Wireless Network, SNR, Wi-Fi, Wireless
- White papers 2006-03-10
- MIMO in 3G Cellular Systems: Challenges and Future Directions
- The multidimensional MIMO channel can be exploited to increase the diversity of the system or to provide parallel spatial channels, which is known as spatial multiplexing. Diversity is generally considered lower risk, and a well-known example is space-time codes, which have found adoption in 3G CDMA cellular systems. Diversity increases...
- Tags: MIMO, Diversity, IEEE, 3G, Cellular Phones, Wireless, Consumer Electronics, Personal Technology
- White papers 2005-04-29
- Space-Frequency Coded Broadband OFDM Systems
- Space-time coding for fading channels is a communication technique that realizes the diversity benefits of multiple transmit antennas. Previous work in this area has focused on the narrowband flat fading case where spatial diversity only in available. This paper investigates the use of space-coding in OFDM-based broadband systems where both...
- Tags: Stanford University, Broadband, OFDM, Broadband Internet, Network Technology, Telecommunications, Wireless, Networking
- White papers
- Diversity Reception for OFDM Systems Using Antenna Arrays
- Orthogonal Frequency Division Multiplexing OFDM is a multicarrier modulation scheme that achieves high spectral efficiency by using minimally densely spaced orthogonal subcarriers without increasing the transmitter and receiver complexities. Antenna arrays are a powerful means to exploit the spatial domain to provide an extra layer of co-channel interference cancellation and...
- Tags: IEEE, Array-OFDM System, OFDM, Wireless
- White papers 2005-12-01
- Multimedia Communication Over OFDM Mobile Wireless Networks: A Cross-Layer Diversity Approach
- Diversity can be used to combat multipath fading and improve the performance of mobile wireless multimedia communication systems. In this work, by considering transmission of an embedded bitstream over a slow varying Rayleigh faded environment, the authors develop a cross-layer diversity technique which takes advantage of both multiple description source...
- Tags: Multimedia, University Of California, OFDM, Productivity, Wireless
- White papers
- Select strong passwords that baffle the bad guys: Apply the principle of character diversity
- Character diversity is a key component of strong passwords. By using many types of characters, we reduce the predictability and weakness of our passwords. In other words, increasing the types of characters we use greatly increases our chances of building unique passwords that are more difficult (i.e. take longer) to...
- Tags: Password, Character Diversity
- Book chapters 2006-10-18
- ITIL: Qualification Scheme
- The ITIL qualification scheme is the only training and qualification scheme leading to official ITIL qualification in IT Service Management. It is endorsed by OGC and itSMF international, and by two existing Examinations Institutes: EXIN and ISEB. This paper explains the operation of the ITIL qualification scheme. It describes the...
- Tags: Qualification, ITIL, Process Improvement, It Services, Quality, Business Operations
- White papers 2005-08-01
- Optimizing Voice-Over-IP Speech Quality Using Path Diversity
- In last few years, Voice over Internet Protocol VoIP has been gaining popularity as an alternative to traditional telephone by transmitting voice signals as packets over the Internet and private IP-based networks. However, voice packets experience loss, delay, and delay variation, which require buffering, playout scheduling and loss concealment at...
- Tags: McGill University, IP, Telephony, VOIP, Network Technology, Telecommunications, Networking
- White papers 2006-06-30
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