Do my WiFi and Extender use different spreading codes? - Page 1
Forum section: electronics / rf-microwave

author: cspwcspw
author_rank: Newbie
timestamp: June 03, 2019, 07:21:41 am
content: Hi - I have three related questions. My WiFi and my WiFi Extender use the same WiFi channel, apparently (according to stuff I can find on the Internet) because the extender's job is to relay the signal rather than to regenerate fresh packets for another hop. I'm not certain I trust that explanation ...Q1) WiFi is a spread-spectrum mechanism. Would it use the same spreading/hopping codes for all connected devices in my home network, or does each connection get its own spreading code? I think capturing wireless packets with Wireshark (or broadcast mechanism) shows me all the wireless traffic, so I suspect we're all using the same spreading/hopping code.Q2) Would an access point ever simultaneously broadcast or receive from more than one client, or are packets time-interleaved rather than simultaneous?Q3) Would my typical WiFi extender use the same spreading as the primary access point?Thanks if you can help, fix my confusions, or point me in the right direction.Peter

author: OwO
author_rank: Super Contributor
timestamp: June 03, 2019, 09:56:29 am
content: Wifi hasn't used spread spectrum since b, and even when it did it used a fixed code. The only mechanism of multiple access is TDMA, and a poor one at that (listen before talk). Two conversations can NOT happen on one wifi channel simultaneously, they have to wait for their turn.

author: LapTop006
author_rank: Unknown
timestamp: June 03, 2019, 10:11:18 am
content: Quote from: OwO on June 03, 2019, 09:56:29 amMU-MIMOstarts to somewhat change this, although there'smanypractical limitations on it.I'm of the camp that just runs UTP to all my access points, and all my fixed devices are cabled too, so my non-fixed devices (laptop, etc.) can get better results.

author: NiHaoMike
author_rank: Super Contributor
timestamp: June 03, 2019, 03:42:33 pm
content: The better extenders have separate radios for AP and backhaul. It used to be common to build your own by connecting a router in client mode to another router in AP mode, but nowadays you can just buy a dual band extender.

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: June 04, 2019, 08:56:36 am
content: Range extenders can sometimes make things worse (EG in dense populated areas) because it takes a congested network hurting performance and congests it some more.

author: NiHaoMike
author_rank: Super Contributor
timestamp: June 04, 2019, 07:40:06 pm
content: Quote from: TheUnnamedNewbie on June 04, 2019, 08:56:36 amThe dual radio extenders don't halve the bandwidth like the really cheap ones do.

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: June 05, 2019, 04:59:10 am
content: Quote from: NiHaoMike on June 04, 2019, 07:40:06 pmThat is not the problem I was talking about (but indeed still a problem). During my student job, I often ran in to cases where a person, let's call em' Alice, lived in an apartment building. Alice didn't have good wifi reception in say her bedroom. They talk about it with their neighbour, Bob, who says they had issues too and so bought a range extender. Alice decided to do that. They come home, install the access point, but now still have issues. I get called up (as IT tech), and I run a network scan, and find more than 70 networks in their building. The problem: Everyone has wifi blasting out full, and then to get even the smallest bit of reception, they need a billion range extenders on to of that, and now their spectrum is congested with re-transmits of re-transmits and announce packets. And because their extender re transmits everything it gets, It will try to re transmit all those packages too on another band, just making the problem worse. If everyone in the building starts doing that, it is a miracle you can get a list of networks in the first place. This is why those distributed-access-points spaced around the house using ethernet or power-line communications to talk to a core box is gonna give you much better performance. In fact, the way to alleviate such congestion problems, I think (not an expert), is to place much more access points (not extenders), but lower down their output power and put them in different bands. Kinda the same thing they do with nano/attocells in 4G/LTE/5G

author: David Hess
author_rank: Super Contributor
timestamp: June 06, 2019, 01:52:38 am
content: Quote from: cspwcspw on June 03, 2019, 07:21:41 amA single access point cannot transmit and receive in the same band because out of channel noise from the transmitter overloads the receiver. This is why in-band RF repeaters need a cavity filters for both the receiver and the transmitter. For separate APs, it depends on how close they are.Large installations where multiple APs are in close proximity may synchronize their transmitters so that they all transmit at once.Quote from: OwO on June 03, 2019, 09:56:29 amThis is not strictly true anymore with MIMO. Multiple antennas on a transmitter and receiver can direct their transmit and receive radiation patterns to avoid other transmissions. But a receiver still cannot operate in close proximity to a transmitter.