Nt1310 Unit 1

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Pages: 3

IV. MU-MIMO
One of the key reasons leading to data transmissions using gigabit speeds is the introduction of the multiuser multiple-input multiple-output (MU-MIMO). The paper mentions the effect of increasing spatial streams on the technology cost. Increasing the number of spatial streams even though it greatly helps greater throughputs, it requires an increase in the number of transmitter and receiver antennas thus increasing the cost. Another, issue with the increase in the number of radio chains is the increased requirement of power. These factors have greatly influenced the use of single spatial streams for data transmission. The increase in the number of spatial streams has a direct effect on the data rate [3]. The concept of MU-MIMO allows an access point to communicate with multiple clients using single spatial streams or communicate with a single client using multiple spatial streams. 802.11ac in the MU-MIMO mode supports upto four different users simultaneously. But this is possible only on the downlink [1] [3] [4]. Figure 2 explains the pictorially explains the concept of MU-MIMO using 4 antennas.
V.
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Wider channel widths are obtained by channel bonding. 802.11ac devices support the use of 20 MHz, 40 MHz and 80 MHz as mandatory. Apart from these channel bandwidths, support for 160 MHz is optional [1]. Channel Bonding is a method of increasing channel width by bonding adjacent channels within a given frequency band. Channel bonding increases the number of sub-carriers available for data transmission thus increasing the data rate [4]. In 802.11ac, a channel width of 80 MHz and an optional width of 160 MHz is used. 160 MHz channel width can be formed from two contiguous or non-contiguous 80 MHz channels. If the channels are contiguous then it is called as 160 MHz and if the channels are non-contiguous then it is called as (80+80) MHz [1]