Conference noted::wireless_lans

327.0. "Coverage Area and Throughput Problem" by HGOVC::LAWRENCEWAN () Fri Jan 24 1997 02:05

    Hi All,
    
    	I have a customer who raise a problem about the RoamAbout FH
    PCcards. The following is the summary of his test report.
    
    1.	According to specification DEC RoamAbout, the connection range of
    	the wireless LAN is up to 500 feet, but the result of geographical
    	test at Atrium* show that signal strength** decay exponentially with
    	distance. One RoamAbout Access Point is installed inside the
    	wire-closet adjacent to library. At 120 feet (2/3 distance from 
    	library to book store) from the Access Point, signal decay from 80% 
    	to 30%. While the testing PC move to 170 feet (library to book
    	store) from the Access Point, signal strength remain only 10%.
    	At the point with 30% signal strength, it can provide ftp transfer
    	rate at 22 kbytes/sec. At 10% signal strength, the ftp transfer
    	rate is only 6 kbytes/sec.
    
    2.	Wireless LAN provide 1.6Mbps data rate. The throughput of testing 
    	platform setup at conference room show that the ftp data transfer
    	rate decrease from 37 kbytes/sec for 1 PC to 10 kbyte/sec for 4 PCs
    	when they download file simultaneous.
    
    Detail Testing Report
    
    1.	Geographical test of the RoamAbout At Atrium.
    
    	*Atrium is 200 x 117 feet open area. The AST pentium PC is belong
   	 to classroom sub-net and the file size for ftp test is 1.9M at 
    	 uststf***. The RoamAbout Access Point is located at the
    	 wire-closet outside library.
    
    	** % from the RL2SETUP Test Utility
    	
    	*** HKUST file server name
    
    Location of the Testing PC	Bootup Time	FTP rate	Complete
    								Time
    --------------------------------------------------------------------
    Outside Library
    (Just Beside Access Point)	1 min 44 sec	33.3Kbytes/s	55secs
    
    1/2 from Library to Book
    Store (~100 feet)		1 min 55 sec	30  Kbytes/s	61.28secs
    
    2/3 from Library to Book
    Store (~150 feet)		-		21.5Kbytes/s	86.7secs
    
    Outside Book Store
    (~180 feet)			-		5   Kbytes/s	373secs
    
    Escalator to Academic 
    Concourse (~130 feet)
    (AS diagonal of Atrium)	-		12  Kbytes/s	157secs
    
    Outside Lift 2		3 min		6   Kbytes/s	311.9secs
    (~180 feet) (As diagonal of Atrium)
    
    
    2.	Throughput Test
    
    	RoamAbout Access Point and PCs are located inside conference room.
    	The file size for ftp test is 1.9M at uststf.
    
    	No. of PC under test		FTP rate	Complete time
    	-----------------------------------------------------------------
    	         1			36.80Kbytes/s	 50.65 secs
    		 2			15.20Kbytes/s	122.64 secs
    		 3			13.33Kbytes/s	139.81 secs
    		 4			10.58Kbytes/s	176.12 secs
    	-----------------------------------------------------------------
    
    From the above test report, they concern that the coverage area of the
    RoamAbout FH PC card and their Throughput when more and more PCs using
    the same Access Point.
    
    
    On the other hand, I also do the test in the same site. The result as
    below:
    
    Distance 	       Throughput (Transmit)	Throughput (Receive)
    ~100 feet	       0.25 to 0.50 Mbits/s     0.34 to 0.41 Mbits/s
    ~180 feet	       0.00 to 0.10 Mbits/s	0.00 to 0.10 Mbits/s
    
    * I use two HINote CS450 and the customer's Access Point run the Bricks
      demo to get this result. The Block Size is 1000000bit.
    
    Regards,
    Lawrence 
    NPBU HGO
    	
     
    	

    Hi Lawrence,
    
    This is slightly less than I would expect but not substantially.  It
    looks like you are seeing peaks of about 300Kb/s using TCPIP.  
    
    First, although the signaling rate is 1.6Mb/s the best you will see for
    actual user throughput is between 40 and 60% of that.  With TCPIP or
    DECnet you will actually see less, since the NOS is burdened with more 
    overhead in doing ACK packets.  If you use NetBEUI or IPX you will see
    as much as twice the throughput do to the way the protocol works.
    
    As for the distance, without knowing the layout I would generally
    expect the coverage area to be around 200 feet.  With the FH product,
    once you get to a level of errors, the radio protocol drops to a
    0.8Mb/s signalling rate to help get a higher % of data through,
    therefore your seeing a lower user throughput.
    
    Regards,
    Jeff
    
    PS: look at our www-wireless.lkg.dec.com homepage 'RoamAbout Frequently
    asked Questions' that has other info that may also be of interest to
    you.