So as we said, one of the initial problems with CDMA was the near-far problem, and that's problem number one. That was the one that we focused most on this lecture, because that concerns how your cellphone determines what it should and shouldn't transmit. And the second problem that they had to overcome was the idea of what's called a Handoff. With Handoffs we're talking about what happens when a device has to switch between two different base stations. So if this is one base station, and this is another base station, what happens when your device is currently talking [SOUND] to this base station? So if you're driving in your car, and you're on your cell phone, but then you move into the coverage area of the next space station. How does it handle that switch to the one that is giving you the better channel quality? Well, under FDMA or TDMA, you switch frequency channels. So this change can happen very quickly, and it's not too much of an issue, to have that happen. So you just, switch frequency channels and switch base stations accordingly. But with CDMA, it's much harder to do that because, first of all, the cells don't have dedicated frequency channels. Everyone's transmitting in the same bands, so it's not as easy as just switching from one channel to another. But the second problem is that when a device enters [SOUND] another cell. The CDM, the power control algorithm are going to have to reconverge very, very, very quickly in order for you not to see any effect on your call quality. Because if you currently have your SIR all figured out, when you're over in this cell, and then you suddenly transition to this new cell tower. Then that algorithm would have to reconverge very quickly to you depending upon the current channel conditions. From all of the other mobile stations that are in this cell, and taking those into account. So, this is known as a Hard Handoff, and again Hard Handoff works fine when you have FDMA or TMA, but for CDMA, we need another solution. We can't use the Hard Handoff. What engineers came up with was the idea of a soft handoff instead. And the scheme of a soft handoff is that when a device, when you're driving in your car and you're currently talking to the cell tower. Rather than this disconnection and reconnection happening very, very quickly in that transition, we do it smoother, and more soft. That's where the term soft versus hard comes from. So, right now you're talking to this tower, and then once you move into the intersection region, you'll actually keep connectivity [SOUND] with this tower. While connecting to the new tower as well. And so you won't just drop the connection really quickly from this tower and you also won't completely rely then on this tower. because that will give the power control algorithm enough time to converge as is necessary for you to then move into this cell to have a smoother transition. A more seamless transition, so you won't notice that it happened, and that's called the Soft Handoff. And that worked very well for CDMA. In fact it works much better withr CDMA than the Hard Handoff works for FDMA or TDMA. because it's much smoother and gives much better transition in call quality.