Sunday, July 24, 2011
Thursday, July 21, 2011
Amrisa Bhagwandin has an interesting post over at goingLTE.com titled Verizon Reserving Its Phones for Its Own Network?
In the post, Amrisa speculates that Verizon Wireless is designing its phones so they will only run on the Verizon Wireless network. Bhagwandin also speculates AT&T may end up doing the same. Here's some of the technical details:
The Verizon Wireless and AT&T 4G Long Term Evolution (LTE) networks run on different frequency bands:
- AT&T runs in the 704-746 Mega Hertz (MHz) band
There is some slight overlap between the two bands but there is not enough overlap for devices to run on each others networks. It's also important to remember the 4G conversion is not going to be like throwing a switch. Tower antennas will be gradually updated from 3G to 4G. This means 4G phones have both 3G and 4G radios in them - the 4G radio is used when 4G service is available and the 3G radio is used when 4G service is not available. This fallback also causes a problem. In locations where 4G service is not available, Verizon phones will fall back on the Verizon wireless CDMA 3G network and AT&T phones will fall back on the AT&T HSPA/GSM 3G network.
- Verizon Wireless runs in the 746-787 MHz band
And..... it gets even more complicated - both Verizon Wireless and AT&T both own spectrum through MetroPCS and Bhagwandin thinks we'll see both companies setting up sales through MetroPCS to try and lock customers into their networks . In addition, we may see similar deals being made with Lightsquared and Cricket since both of these companies are developing their own 4G networks.
I'm in wait-and-see mode right now and not going to lock into any new long term wireless contracts until I get a better idea of how it is all going to shake out.
Monday, July 18, 2011
Here's what I love about Google+ in general and the Google+ Diet in particular:I haven't personally ditched any of my other social media yet but I do find myself going to Google+ more and using Facebook and Twitter less frequently.
Instead of saying, "I'm going to write a blog post now," or "I'm going to send an e-mail" or "I think I'll tweet something" you simply say what you have to say, then decide who you're going to say it to.
If you address it to "Public," it's a blog post.
If you address it to "Your Circles" it's a tweet.
If you address it to your "My Customers" Circle it's a business newsletter.
If you address it to a single person, it can be a letter to your mother.
I'd say this is pretty revolutionary.
You can follow Mike's Google+ Diet experiment here. My Google+ public stream is linked here.
Friday, July 15, 2011
Thursday, July 14, 2011
Since the early 1900’s the infrastructure has been tuned to match these frequency requirements using devices called loading coils.
Both George Campbell at AT&T and Michael Pupin at Columbia University were working in 1899 on wire pair mutual capacitance problem. Both realized that, by adding a lump series inductance called a loading coil, resonance could be used to cancel the effects of shunt capacitive reactance and increase signal strength over long local loops. Michael Pupin ended up getting the patent and by late 1899 loading coils were being installed in the field on copper wire pairs longer than 3 miles.
D = 6000 feet ≈ 1 mile
C = .083 μF/mile
In addition to H (6000 ft) load coil spacing, there are also B (3000 ft) spacing and D (4500 ft) spacing loading coils. By changing coil spacing along with coil inductance the loop cutoff frequency can be adjusted or tuned to the proper value. Let's look at another example.
D = 3000 feet ≈ .5 miles
C = .083 μF/mile
Monday, July 11, 2011
I know this post gets a little mathematical. Try and think of the math in simple terms - in the examples below we're dealing with some basic division:
That's numerator (top number) divided by denominator (bottom number) in the equation.
If the numerator is large compared to the denominator then the answer is going to be relatively large (think big number divided by small number gives big number answer and remember...... everything is relative :) ). And vice versa - if the numerator is small compared to the denominator then the answer is going to be small ((think small number divided by big number gives small number answer).
This should help to understand the examples below.
In my last post I wrote about the local loop - that pair of copper telephone wires most of us still have coming into out homes.These wires have been used for voice in some places for close to 100 years and now, using DSL technologies, to deliver voice and data. AT&T UVerse is even using the local loop to deliver triple play services - voice, video and data. In this post, let's take a little close look transmission lines.
The local telephone loop (also referred to as the subscriber loop) is the dedicated copper wire twisted pair connecting a telephone company Central Office (CO) in a locality to a customer home or business. The loop resistance is critical in the local loop and phone companies have had to “tune” the loop to transmit high-quality voice. Typically, companies have used 19 gauge (1.25 decibels [dB] attenuation per mile) to 26 gauge (3 dB attenuation per mile) copper wire for the local loop. The average customer local loop is about 2 miles and attenuation on this loop is ideally kept below 8 dB.
We can look at a typical transmission line model and use it to represent a subscriber loop:
We can see that the inductance (L), resistances (R for series resistance and S for shunt resistance), and capacitance (C) are distributed throughout the model. We can also show that these values cause signal loss and distortion. A local loop copper wire pair effectively forms a capacitance since you have two conductors (copper wire) separated by an insulator (wire insulation). Shunt or mutual capacitive reactance is independent of wire gauge and local loop wire pairs designed for voice have a capacitance value of about .083 μF/mile.
In addition to local loop cable, copper cables designed for higher frequencies like those used for T carrier systems are designed to provide a capacitance of .066 μF/mile.
Capacitive reactance is basically the resistance of a capacitance and it changes with frequency. The formula for capacitive reactance is:
The units for capacitive reactance are Ohms (Ω). Looking at the formula you can see as frequency increases the denominator gets larger so the capacitive reactance drops. On long local loops (3 miles and greater) shunt capacitance values increase to the point where significant signal leakage occurs at frequencies greater than 1000 Hz. If you look at the formula, you realize the higher the frequency the greater the leakage loss. Let’s look at some examples:
A local loop is 1 mile long. Calculate the capacitive reactance for the loop at 2KHz.
Using f = 2 KHz
This same local loop is extended to 3 miles. Calculate the new capacitive reactance for the loop at 2KHz
Using f = 2 KHz
In the example you can see that, by increasing the length of the loop by two miles, shunt capacitance drops by a factor close to 10.
In addition to length, higher frequencies also cause shunt capacitance reactance to increase.
Let’s increase the frequency in Example B to 3KHz and calculate the capacitive reactance of the local loop.
Using f = 3 KHz
Let’s now decrease the frequency to 1KHz and calculate the capacitive reactance of the local loop.
Using f = 1 KHz
Now consider a voice conversation on the Example C local loop. We know the frequency range of the local loop is approximately 300 Hz to 3300 Hz. We know the human voice can produce frequencies of both 3KHz and 1KHz and the average ear can hear these frequencies. At 1 KHz we have a shunt capacitive reactance of 639Ω and at 3 KHz we have a shunt capacitive reactance of 213Ω. You can see more signal is lost due to capacitive shunting at the higher frequencies than at the lower frequencies. When it comes to voice - the listener will notice these differences – the lower frequencies in a voice conversation will appear louder than the higher frequencies in a conversation.
Over 100 years ago telephone companies figured out they could "load" a transmission line with inductors (loading coils) to reduce the effects of capacitive reactance. I'll discuss loading coils in a future post.